In defence of lobbying

Lobbying of politicians has acquired a dirty name, and that’s a pity. In fact, I find it rather irritating. Lobbying means campaigning, providing expert analysis and briefing to politicians, who are usually generalists and need that guidance from experts. Good politicians even come looking for it, to gain a better understanding of complex problems.

That’s when lobbying is being done well and responsibly. Some of my recent work counts as lobbying, related to the law of evidence in England and the Post Office Horizon scandal. I’m proud of that. It is a worthwhile activity and can help the political process work better.

Lobbying is quite different from schmoozing old pals to give other chums contracts without the tedious bureaucracy of open tenders. It’s different from offering politicians highly paid sinecures in the hope they’ll work on behalf of you rather than their constituents. It is certainly different from handing out bribes. Lobbying is not the same as corruption, and that is what we’ve been seeing lately in the UK.

Bugs are about more than code

Bugs are about more than code


Recently I have had to think carefully about the nature of software systems, especially complex ones, and the bugs they contain. In doing so my thinking has been guided by certain beliefs I hold about complex software systems. These beliefs, or principles, are based on my practical experience but also on my studies, which, as well as teaching me much that I didn’t know, have helped me to make sense of what I have done and seen at work. Here are three vital principles I hold to be true.

Principle 1

Complex systems are not like calculators, which are predictable, deterministic instruments, i.e. they will always give the same answer from the same inputs. Complex systems are not predictable. We can only predict what they will probably do, but we cannot be certain. It is particularly important to remember this when working with complex socio-technical systems, i.e. complex systems, in the wider sense, that include humans, which are operated by people or require people to make them work. That covers most, or all, complex software systems.

Principle 2

Complex systems are more than the sum of their parts, or at least they are different. A system can be faulty even if all the individual programs,or components, are working correctly. The individual elements can combine with each other, and with the users, in unexpected and possibly damaging ways that could not have been predicted from inspecting the components separately.

Conversely, a system can be working satisfactorily even if some of the components are flawed. This inevitably means that the software code itself, however important it is, cannot be the only factor that determines the quality of the system.

Principle 3

Individual programs in a system can produce harmful outcomes even if their code was written perfectly. The outcome depends on how the different components, factors and people work together over the life of the system. Perfectly written code can cause a failure long after it` has been released when there are changes to the technical, legal, or commercial environment in which the system runs.

The consequences

Bugs in complex systems are therefore inevitable. The absence of bugs in the past does not mean they are absent now, and certainly not that the system will be bug free in the future. The challenge is partly to find bugs, learn from them, and help users to learn how they can use the system safely. But testers should also try to anticipate future bugs, how they might arise, where the system is vulnerable, and learn how and whether users and operators will be able to detect problems and respond. They must then have the communication skills to explain what they have found to the people who need to know.

What we must not do is start off from the assumption that particular elements of the system are reliable and that any problems must have their roots elsewhere in the system. That mindset tends to push blame towards the unfortunate people who operate a flawed system.

Bugs and the Post Office Horizon scandal

justice lost in the postOver the last few months I have spent a lot of time on issues raised by the Post Office Horizon scandal. For a detailed account of the scandal I strongly recommend the supplement that Private Eye has produced, written by Richard Brooks and Nick Wallis, “Justice lost in the post”.

When I have been researching this affair I have realised, time and again, how the Post Office and Fujitsu, the outsourced IT services supplier, ignored the three principles I outlined. While trawling through the judgment of Mr Justice Fraser in Bates v Post Office Ltd (No 6: Horizon Issues, i.e. the second of the two court cases brought by the Justice For Subpostmasters Alliance), which should be compulsory reading for Computer Science students, I was struck by the judge’s discussion of the nature of bugs in computer systems. You can find the full 313 page judgment here [PDF, opens in new tab].

The definition of a bug was at the heart of the second court case. The Post Office, and Fujitsu (the outsourced IT services supplier) argued that a bug is a coding error, and the word should not apply to other problems. The counsel for the claimants, i.e. the subpostmasters and subpostmistresses who had been victims of the flawed system, took a broader view; a bug is anything that means the software does not operate as users, or the corporation, expect.

After listening to both sides Fraser came down emphatically on the claimants’ side.

“26 The phrase ‘bugs, errors or defects’ is sufficiently wide to capture the many different faults or characteristics by which a computer system might not work correctly… Computer professionals will often refer simply to ‘code’, and a software bug can refer to errors within a system’s source code, but ‘software bugs’ has become more of a general term and is not restricted, in my judgment, to meaning an error or defect specifically within source code, or even code in an operating system.

Source code is not the only type of software used in a system, particularly in a complex system such as Horizon which uses numerous applications or programmes too. Reference data is part of the software of most modern systems, and this can be changed without the underlying code necessarily being changed. Indeed, that is one of the attractions of reference data. Software bug means something within a system that causes it to cause an incorrect or unexpected result. During Mr de Garr Robinson’s cross-examination of Mr Roll, he concentrated on ‘code’ very specifically and carefully [de Garr Robinson was the lawyer representing the Post Office and Roll was a witness for the claimants who gave evidence about problems with Horizon that he had seen when he worked for Fujitsu]. There is more to the criticisms levelled at Horizon by the claimants than complaints merely about bugs within the Horizon source code.

27 Bugs, errors or defects is not a phrase restricted solely to something contained in the source code, or any code. It includes, for example, data errors, data packet errors, data corruption, duplication of entries, errors in reference data and/or the operation of the system, as well as a very wide type of different problems or defects within the system. ‘Bugs, errors or defects’ is wide enough wording to include a wide range of alleged problems with the system.”

The determination of the Post Office and Fujitsu to limit the definition of bugs to source code was part of a policy of blaming users for all errors that were not obviously caused by the source code. This is clear from repeated comments from witnesses and from Mr Justice Fraser in the judgment. “User error” was the default explanation for all problems.

This stance was taken to an extreme with “phantom transactions”. These were transactions generated by the system but which were recorded as if they had been made by a user (see in particular paragraphs 209 to 214 of Fraser’s judgment).

In paragraph 212 Fraser refers to a Fujitsu problem report.

“However, the conclusion reached by Fujitsu and recorded in the PEAK was as follows:

‘Phantom transactions have not been proven in circumstances which preclude user error. In all cases where these have occurred a user error related cause can be attributed to the phenomenon.'”

This is striking. These phantom transactions had been observed by Royal Mail engineers. They were known to exist. But they were dismissed as a cause of problems unless it could be proven that user error was not responsible. If Fujitsu could imagine a scenario where user error might have been responsible for a problem they would rule out the possibility that a phantom transaction could have been the cause, even if the phantom had occurred. The PEAK (error report) would simply be closed off, whether or not the subpostmaster agreed.

This culture of blaming users rather than software was illustrated by a case of the system “working as designed” when its behaviour clearly confused and misled users. In fact the system was acting contrary to user commands. In certain circumstances if a user entered the details for a transaction, but did not commit it, the system would automatically complete the transaction with no further user intervention, which might result in a loss to the subpostmaster.

The Post Office, in a witness statement, described this as a “design quirk”. However, the Post Office’s barrister, Mr de Garr Robinson, in his cross-examination of Jason Coyne, an IT consultant hired by the subpostmasters, was able to convince Nick Wallis (one of the authors of “Justice lost in the post”) that there wasn’t a bug.

“Mr de Garr Robinson directs Mr Coyne to Angela van den Bogerd’s witness statement which notes this is a design quirk of Horizon. If a bunch of products sit in a basket for long enough on the screen Horizon will turn them into a sale automatically.

‘So this isn’t evidence of Horizon going wrong, is it?’ asks Mr de Garr Robinson. ‘It is an example of Horizon doing what it was supposed to do.’

‘It is evidence of the system doing something without the user choosing to do it.’ retorts Mr Coyne.

But that is not the point. It is not a bug in the system.”

Not a bug? I would contest that very strongly. If I were auditing a system with this “quirk” I would want to establish the reasons for the system’s behaviour. Was this feature deliberately designed into the system? Or was it an accidental by-product of the system design? Whatever the answer, it would be simply the start of a more detailed scrutiny of technical explanations, understanding of the nature of bugs, the reasons for a two-stage committal of data, and the reasons why those two stages were not always applied. I would not consider “working as designed” to be an acceptable answer.

The Post Office’s failure to grasp the nature of complex systems

A further revealing illustration of the Post Office’s attitude towards user error came in a witness statement provided for the Common Issues trial, the first of the two court cases brought by the Justice For Subpostmasters Alliance. This first trial was about the contractual relationship between the Post Office and subpostmasters. The statement came from Angela van den Bogerd. At the time she was People Services Director for the Post Office, but over the previous couple of decades she had been in senior technical positions, responsible for Horizon and its deployment. She described herself in court as “not an IT expert”. That is an interesting statement to consider alongside some of the comments in her witness statement.

“[78]… the Subpostmaster has complete control over the branch accounts and transactions only enter the branch accounts with the Subpostmaster’s (or his assistant’s) knowledge.

[92] I describe Horizon to new users as a big calculator. I think this captures the essence of the system in that it records the transactions inputted into it, and then adds or subtracts from the branch cash or stock holdings depending on whether it was a credit or debit transaction.”

“Complete control”? That confirms her admission that she is not an IT expert. I would never have been bold, or reckless, enough to claim that I was in complete control of any complex IT system for which I was responsible. The better I understood the system the less inclined I would be to make such a claim. Likening Horizon to a calculator is particularly revealing. See Principle 1 above. When I have tried to explain the nature of complex systems I have also used the calculator analogy, but as an illustration of what a complex system is not.

If a senior manager responsible for Horizon could use such a fundamentally mistaken analogy, and be prepared to insert it in a witness statement for a court case, it reveals how poorly equipped the Post Office management was to deal with the issues raised by Horizon. When we are confronted by complexity it is a natural reaction to try and construct a mental model that simplifies the problems and makes them understandable. This can be helpful. Indeed it is often essential if we are too make any sense of complexity. I have written about this here in my blog series “Dragons of the unknown”.

However, even the best models become dangerous if we lose sight of their limitations and start to think that they are exact representations of reality. They are no longer fallible aids to understanding, but become deeply deceptive.

If you think a computer system is like a calculator then you will approach problems with the wrong attitude. Calculators are completely reliable. Errors are invariably the result of users’ mistakes, “finger trouble”. That is exactly how senior Post Office managers, like Angela van den Bogerd, regarded the Horizon problems.


The Horizon scandal has implications for the argument that software developers can produce systems that have no bugs, that zero bugs is an attainable target. Arlo Belshee is a prominent exponent of this idea, of BugsZero as it is called. Here is a short introduction.

Before discussing anyone’s approach to bugs it is essential that we are clear what they mean by a bug. Belshee has a useful definition, which he provided in this talk in Singapore in 2016. (The conference website has a useful introduction to the talk.)

3:50 “The definition (of a bug) I use is anything that would frustrate, confuse or annoy a human and is potentially visible to a human other than the person who is currently actively writing (code).”

This definition is close to Justice Fraser’s (see above); “a bug is anything that means the software does not operate as users, or the corporation, expect”. However, I think that both definitions are limited.

BugsZero is a big topic, and I don’t have the time or expertise to do it justice, but for the purposes of this blog I’m happy to concede that it is possible for good coders to deliver exactly what they intend to, so that the code itself, within a particular program, will not act in ways that will “frustrate, confuse or annoy a human”, or at least a human who can detect the problem. That is the limitation of the definition. Not all faults with complex software will be detected. Some are not even detectable. Our inability to see them does not mean they are absent. Bugs can produce incorrect but plausible answers to calculations, or they can corrupt data, without users being able to see that a problem exists.

I speak from experience here. It might even be impossible for technical system experts to identify errors with confidence. It is not always possible to know whether a complex system is accurate. The insurance finance systems I used to work on were notoriously difficult to understand and manipulate. 100% accuracy was never a serious, practicable goal. As I wrote in “Fix on failure – a failure to understand failure”;

“With complex financial applications an honest and constructive answer to the question ‘is the application correct?’ would be some variant on ‘what do you mean by correct?’, or ‘I don’t know. It depends’. It might be possible to say the application is definitely not correct if it is producing obvious garbage. But the real difficulty is distinguishing between the seriously inaccurate, but plausible, and the acceptably inaccurate that is good enough to be useful. Discussion of accuracy requires understanding of critical assumptions, acceptable margins of error, confidence levels, the nature and availability of oracles, and the business context of the application.”

It is therefore misleading to define bugs as being potentially visible to users. Nevertheless, Belshee’s definition is useful provided that qualifiction is accepted. However, in the same talk, Belshee goes on to make further statements I do not accept.

19:55 “A bug is an encoded developer mistake.”

28:50 “A bug is a mistake by a developer.”

This is a developer-centric view of systems. It is understandable if developers focus on the bugs for which they are responsible. However, if you look at the systems, and bugs, from the other end, from the perspective of users when a bug has resulted in frustration, confusion or annoyance, the responsibility for the problem is irrelevant. The disappointed human is uninterested in whether the problem is with the coding, the design, the interaction of programs or components, or whatever. All that matters is that the system is buggy.

There is a further complication. The coder may well have delivered code that was perfect when it was written and released. But perfect code can create later problems if the world in which it operates changes. See Principle 3 above. This aspect of software is not sufficiently appreciated; it has caused me a great deal of trouble in my career (see the section “Across time, not just at a point in time” in this blog, about working with Big Data).

Belshee does say that developers should take responsibility for bugs that manifest themselves elswhere, even if their code was written correctly. He also makes it clear, when talking about fault tolerant systems (17:22 in the talk above), that faults can arise “when the behaviour of the world is not as we expect”.

However he also says that the system “needs to work exactly as the developer thought if it’s going to recover”. That’s too high a bar for complex socio-technical systems. The most anyone can say, and it’s an ambitious target, is that the programs have been developed exactly as the developers intended. Belshee is correct at the program level; if the programs were not built as the developers intended then recovery will be very much harder. But at the system level we need to be clear and outspoken about the limits of what we can know, and about the inevitability that bugs are present.

If we start to raise hopes that systems might be perfect and bug-free because we believe that we can deliver perfectly written code then we are setting ourselves up for unpleasant recriminations when our users suffer from bugs. It is certainly laudable to eradicate sloppy and cavalier coding and it might be noble for developers to be willing to assume responsibility for all bugs. But it could leave them exposed to legal recriminations if the wider world believes that software developers can and should` ensure systems are free of bugs. This is where lawyers might become involved and that is why I’m unhappy about the name BugsZero, and the undeliverable promise that it implies.

Unnoticed and undetectable bugs in the Horizon case

The reality that a bug might be real and damaging but not detected by users, or even detectable by them, was discussed in the Horizon case.

“[972] Did the Horizon IT system itself alert Subpostmasters of such bugs, errors or defects… and if so how?

[973] Answer: Although the experts were agreed that the extent to which any IT system can automatically alert its users to bugs within the system itself is necessarily limited, and although Horizon has automated checks which would detect certain bugs, they were also agreed that there are types of bugs which would not be detected by such checks. Indeed, the evidence showed that some bugs lay undiscovered in the Horizon system for years. This issue is very easy, therefore, to answer. The correct answer is very short. The answer… is ‘No, the Horizon system did not alert SPMs’. The second part of the issue does not therefore arise.”

That is a significant extract from an important judgment. A senior judge directly addressed the question of system reliability and pronounced that he is satisfied that a complex system cannot be expected to have adequate controls to warn users of all errors.

This is more than an abstract, philosophical debate about proof, evidence and what we can know. In England there is a legal presumption that computer evidence is reliable. This made a significant contribution to the Horizon scandal. Both parties in a court case are obliged to disclose documents which might either support or undermine their case, so that the other side has a chance to inspect and challenge them. The Post Office and Fujitsu did not disclose anything that would have cast doubt on their computer evidence. That failure to disclose meant it was impossible for the subpostmasters being prosecuted to challenge the presumption that the evidence was reliable. The subpostmasters didn’t know about the relevant system problems, and they didn’t even know that that knowledge had been withheld from them.

Replacing the presumption of computer reliability

There are two broad approaches that can be taken in response to the presumption that computer evidence is reliable and the ease with which it can be abused, apart of course from ignoring the problem and accepting that injustice is a price worth paying for judicial convenience. England can scrap the presumption, which would require the party seeking to use the evidence to justify its reliability. Or the rules over disclosure can be strengthened to try and ensure that all relevant information about systems is revealed. Some blend of the two approaches seems most likely.

I have recently contributed to a paper entitled “Recommendations for the probity of computer evidence”. It has been submitted to the Ministry of Justice, which is responsible for the courts in England & Wales, and is available from the Digital Evidence and Electronic Signature Law Review.

The paper argues that the presumption of computer reliability should be replaced by a two stage approach when reliability is challenged. The provider of the data should first be required to provide evidence to demonstrate that they are in control of their systems, that they record and track all bugs, fixes, changes and releases, and that they have implemented appropriate security standards and processes.

If the party wishing to rely on the computer evidence cannot provide a satisfactory response in this first stage then the presumption of reliability should be reversed. The second stage would require them to prove that none of the failings revealed in the first stage might affect the reliability of the computer evidence.

Whatever approach is taken, IT professionals would have to offer an opinion on their systems. How reliable are the systems? What relevant evidence might there be that systems are reliable, or unreliable? Can they demonstrate that they are in control of their systems? Can they reassure senior managers who will have to put their name to a legal document and will be very keen to avoid the humiliation that has been heaped upon Post Office and Fujitsu executives, with the possibility of worse to come?

A challenging future

The extent to which we can rely on computers poses uncomfortable challenges for the English law now, but it will be an increasingly difficult problem for the IT world over the coming years. What can we reasonably say about the systems we work with? How reliable are they? What do we know about the bugs? Are we sufficiently clear about the nature of our systems to brief managers who will have to appear in court, or certify legal documents?

It will be essential that developers and testers are clear in their own minds, and in their communications, about what bugs are. They are not just coding errors, and we must try to ensure people outside IT understand that. Testers must also be able to communicate clearly what they have learned about systems, and they must never say or do anything that suggests systems will be free of bugs.

Testers will have to think carefully about the quality of their evidence, not just about the quality of their systems. How good is our evidence? How far can go in making confident statements of certainty? What do we still not know, and what is the significance of that missing knowledge? Much of this will be a question of good management. But organisations will need good testers, very good testers, who can explain what we know, and what we don’t know, about complex systems; testers who have the breadth of knowledge, the insight, and the communication skills to tell a convincing story to those who require the unvarnished truth.

We will need confident, articulate testers who can explain that a lack of certainty about how complex systems will behave is an honest, clear sighted, statement of truth. It is not an admission of weakness or incompetence. Too many people people in IT have build good careers on bullshitting, on pretending they are more confident and certain than they have any right to be. Systems will inevitably become more complex. IT people will increasingly be dragged into litigation, and as the Post Office and Fujitsu executives have found, misplaced and misleading confidence and bluster in court have excruciating personal consequences. Unpleasant though these consequences are, they hardly compare with the tragedies endured by the subpostmasters and subpostmistresses, whose lives were ruined by corporations who insisted that their complex software was reliable.

The future might be difficult, even stressful, for software testers, but they will have a valuable, essential role to play in helping organisations and users to gain a better understanding of the fallible nature of software. To say the future will be interesting is an understatement; it will present exciting challenges and there should be great opportunities for the best testers.

The Post Office Horizon IT scandal, part 2 – evidence & the “off piste” issue

In the first post of this three part series about the scandal of the Post Office’s Horizon IT system I explained the concerns I had about the approach to errors and accuracy. In this post I’ll talk about my experience working as an IT auditor investigating frauds, and my strong disapproval for the way the Post Office investigated and prosecuted the Horizon cases.

Evidence, certainty and prosecuting fraud

Although I worked on many fraud cases that resulted in people going to prison I was never required to give evidence in person. This was because we built our case so meticulously, with an overwhelmingly compelling set of evidence, that the fraudsters always pleaded guilty rather than risk antagonising the court with a wholly unconvincing plea of innocence.

We always had to be aware of the need to find out what had happened, rather than simply to sift for evidence that supported our working hypothesis. We had to follow the trail of evidence, but remain constantly alert to the possibility we might miss vital, alternative routes that could lead to a different conclusion. It’s very easy to fall quickly into the mindset that the suspect is definitely guilty and ignore anything that might shake that belief. Working on these investigations gave me great sympathy for the police carrying out detective work. If you want to make any progress you can’t follow up everything, but you have to be aware of the significance of the choices you don’t make.

In these cases there was a clear and obvious distinction between the investigators and the prosecutors. We, the IT auditors, would do enough investigation for us to be confident we had the evidence to support a conviction. We would then present that package of evidence to the police, who were invariably happy to run with a case where someone else had done the leg work. The police would do some confirmatory investigation of their own, but it was our work that would put people in jail. The prosecution of the cases was the responsibility of the Crown Prosecution Service in England & Wales, and the Procurator Fiscal Service in Scotland. That separation of responsibilities helps to guard against some of the dangers that concerned me about bias during investigation.

This separation didn’t apply in the case of the Post Office, which for anachronistic, historical reasons, employs its own prosecutors. It also has its own investigation service. There’s nothing unusual about internal investigators, but when they are working with an in house prosecution service that creates the danger of unethical behaviour. In the case of the Post Office the conduct of prosecutions was disgraceful.

The usual practice was to charge a sub-postmaster with theft and false accounting, even if the suspect had flagged up a problem with the accounts and there was no evidence that he or she had benefitted from a theft, or even committed one. Under pressure sub-postmasters would usually accept a deal. The more serious charge of theft would be dropped if they pleaded guilty to false accounting, which would allow the Post Office to pursue them for the losses.

What made this practice shameful was that the Post Office knew it had no evidence for theft that would secure a conviction. This doesn’t seem to have troubled them. They knew the suspects were guilty. They were protecting the interests of the Post Office and the end justified the means.

The argument that the prosecution tactics were deplorable is being taken very seriously. The Criminal Cases Review Commission has referred 39 Horizon cases for appeal, on the grounds of “abuse of process” by the prosecution.

The approach taken by Post Office investigators and prosecutors was essentially to try and ignore the weakest points of their case, while concentrating on the strongest points. This strikes me as fundamentally wrong. It is unprofessional and unethical. It runs counter to my experience.

Although I was never called to appear as a witness in court, when I was assembling the evidence to be used in a fraud trial I always prepared on the assumption I would have to face a barrister, or advocate, who had been sufficiently well briefed to home in on any possible areas of doubt, or uncertainty. I had to be prepared to face an aggressive questioner who could understand where weak points might lie in the prosecution case. The main areas of concern were where it was theoretically possible that data might have been tampered with, or where it was possible that someone else had taken the actions that we were pinning on the accused. Our case was only as strong as the weakest link in the chain of evidence. I had to be ready to explain why the jury should be confident “beyond reasonable doubt” that the accused was guilty.

Yes, it was theoretically possible that a systems programmer could have bypassed access controls and tampered with the logs, but it was vanishingly unlikely that they could have set up a web of consistent evidence covering many applications over many months, even years, and that they could have done so without leaving any trace.

In any case, these sysprogs lacked the deep application knowledge required. Some applications developers, and the IT auditors, did have the application knowledge, but they lacked the necessary privileges to subvert access controls before tampering with evidence.

The source code and JCL decks for all the fraud detection programs would have been available to the defence so that an expert witness could dissect them. We not only had to do the job properly, we had to be confident we could justify our code in court.

Another theoretical possibility was that another employee had logged into the accused’s account to make fraudulent transactions, but we could match these transactions against network logs showing that the actions had always been taken from the terminal sitting on the accused’s desk during normal office hours. I could sit at my desk in head office and use a network monitoring tool to watch what a suspect was doing hundreds of mile away. In one case I heard a colleague mention that the police were trailing a suspect around Liverpool that afternoon. I told my colleague to get back to the cops and tell them they were following the wrong guy. Our man was sitting at his desk in Preston and I could see him working. Half an hour later the police phoned back to say we were right.

In any case, fanciful speculation that our evidence had been manufactured hit the problem of motive; the accused was invariably enjoying a lifestyle well beyond his or her salary, whereas those who might have tampered with evidence had nothing to gain and a secure job, pension and mortgage to lose.

I’ve tried to explain our mindset and thought processes so that you can understand why I was shocked to read about what happened at the Post Office. We investigated and prepared meticulously in case we had to appear in court. That level of professional preparation goes a long way to explaining why we were never called to give evidence. The fraudsters always put their hands up when they realised how strong the evidence was.

Superusers going “off piste”

One of the most contentious aspects of the Horizon case was the prevalence of Transaction Corrections, i.e. corrections applied centrally by IT support staff to correct errors. The Post Office seems to have regarded these as being a routine part of the system, in the wider sense of the word “system”. But it regarded them as being outside the scope of the technical Horizon system. They were just a routine, administrative matter.

I came across an astonishing phrase in the judgment [PDF, opens in new tab, see page 117], lifted from an internal Post Office document. “When we go off piste we use APPSUP”. That is a powerful user privilege which allows users to do virtually anything. It was intended “for unenvisaged ad-hoc live amendment” of data. It had been used on average about once a day, and was assigned on a permanent basis to the ID’s of all the IT support staff looking after Horizon.

I’m not sure readers will realise how shocking the phrase “off piste” is in that context to someone with solid IT audit experience in a respectable financial services company. Picture the reaction of of a schools inspector coming across an email saying “our teachers are all tooled up with Kalashnikovs in case things get wild in the playground”. It’s not just a question of users holding a superuser privilege all the time, bad though that is. It reveals a lot about the organisation and its systems if staff have to jump in and change live data routinely. An IT shop that can’t control superusers effectively probably doesn’t control much. It’s basic.

Where I worked as an IT auditor nobody was allowed to have an account with which they could create, amend or delete production data. There were elaborate controls applied whenever an ad hoc or emergency change had to be made. We had to be confident in the integrity of our data. If we’d discovered staff having permanent update access to live data, for when they went “off piste”, we’d have raised the roof and wouldn’t have eased off till the matter was fully resolved. And if the company had been facing a court action that was centred on how confident we could be in our systems and data we’d have argued strongly that we should cut our losses and settle once we were aware of the “off piste” problem.

Were the Post Office’s, or Fujitsu’s, internal auditors aware of this? Yes, but they clearly did nothing. If I hadn’t discovered that powerful user privileges were out of control on the first day of a two day, high level, IT installation audit I’d have been embarrassed. It’s that basic. However, the Post Office’s internal auditors don’t have the excuse of incompetence. The problem was flagged up by the external auditors Ernst & Young in 2011. If internal audit was unaware of a problem raised by the external auditors they were stealing their salaries.

The only times when work has ever affected my sleep have been when I knew that the police were going to launch dawn raids on suspects’ houses. I would lie in bed thinking about the quality of the evidence I’d gathered. Had I got it all? Had I missed anything? Could I rely on the data and the systems? I worried because I knew that people were going to have the police hammering on their their front doors at 6 o’clock in the morning.

I am appalled that Post Office investigators and prosecutors could approach fraud investigations with the attitude “what can we do to get a conviction?”. They pursued the sub-postmasters aggressively, knowing the weaknesses in Horizon and the Post Office; that was disgraceful.

In the final post in this series I’ll look further at the role of internal audit, how it should be independent and its role in keeping an eye on risk. In all those respects the Post Office’s internal auditors have fallen short.

The Post Office Horizon IT scandal, part 1 – errors and accuracy

For the last few years I’ve been following the controversy surrounding the Post Office’s accounting system, Horizon. This controls the accounts of some 11,500 Post Office branches around the UK. There was a series of alleged frauds by sub-postmasters, all of whom protested their innocence. Nevertheless, the Post Office prosecuted these cases aggressively, pushing the supposed perpetrators into financial ruin, and even suicide. The sub-postmasters affected banded together to take a civil action against the Post Office, claiming that no frauds had taken place but that the discrepancies arose from system errors.

I wasn’t surprised to see that the sub-postmasters won their case in December 2019, with the judge providing some scathing criticism of the Post Office, and Fujitsu, the IT supplier, who had to pay £57.75 million to settle the case. Further, in March 2020 the Criminal Cases Review Commission decided to refer for appeal the convictions of 39 subpostmasters, based on the argument that their prosecution involved an “abuse of process”. I will return to the prosecution tactics in my next post.

Having worked as an IT auditor, including fraud investigations, and as a software tester the case intrigued me. It had many features that would have caused me great concern if I had been working at the Post Office and I’d like to discuss a few of them. The case covered a vast amount of detail. If you want to see the full 313 page judgment you can find it here [PDF, opens in new tab].

What caught my eye when I first heard about this case were the arguments about whether the problems were caused by fraud, system error, or user error. As an auditor who worked on the technical side of many fraud cases the idea that there could be any confusion between fraud and system error makes me very uncomfortable. The system design should incorporate whatever controls are necessary to ensure such confusion can’t arise.

When we audited live systems we established what must happen and what must not happen, what the system must do and what it must never do. We would ask how managers could know that the system would do the right things, and never do the wrong things. We then tested the system looking for evidence that these controls were present and effective. We would try to break the system, evading the controls we knew should be there, and trying to exploit missing or ineffective controls. If we succeeded we’d expect, at the least, the system to hold unambiguous evidence about what we had done.

As for user error, it’s inevitable that users will make mistakes and systems should be designed to allow for that. “User error” is an inadequate explanation for things going wrong. If the system can’t do that then it is a system failure. Mr Justice Fraser, the judge, took the same line. He expected the system “to prevent, detect, identify, report or reduce the risk” of user error. He concluded that controls had been put in place, but they had failed and that Fujitsu had “inexplicably” chosen to treat one particularly bad example of system error as being the fault of a user.

The explanation for the apparently inexplicable might lie in the legal arguments surrounding the claim by the Post Office and Fujitsu that Horizon was “robust”. The rival parties could not agree even on the definition of “robust” in this context, never mind whether the system was actually robust.

Nobody believed that “robust” meant error free. That would be absurd. No system is perfect and it was revealed that Horizon had a large, and persistent number of bugs, some serious. The sub-postmasters’ counsel and IT expert argued that “robust” must mean that it was extremely unlikely the system could produce the sort of errors that had ruined so many lives. The Post Office confused matters by adopting different definitions at different times, which was made clear when they were asked to clarify the point and they provided an IT industry definition of robustness that sat uneasily with their earlier arguments.

The Post Office approach was essentially top down. Horizon was robust because it could handle any risks that threatened its ability to perform its overall business role. They then took a huge logical leap to claim that because Horizon was robust by their definition it couldn’t be responsible for serious errors at the level of individual branch accounts.

Revealingly, the Post Office and Fujitsu named bugs using the branch where they had first occurred. Two of the most significant were the Dalmellington Bug, discovered at a branch in Ayrshire, and the Callendar Square Bug, also from a Scottish branch, in Falkirk. This naming habit linked bugs to users, not the system.

The Dalmellington Bug entailed a user repeatedly hitting a key when the system froze as she was trying to acknowledge receipt of a consignment of £8,000 in cash. Unknown to her each time she struck the key she accepted responsibility for a further £8,000. The bug created a discrepancy of £24,000 for which she was held responsible.

Similarly, the Callendar Square Bug generated spurious, duplicate financial transactions for which the user was considered to be responsible, even though this was clearly a database problem.

The Horizon system processed millions of transactions a day and did so with near 100% accuracy. The Post Office’s IT expert therefore tried to persuade the judge that the odds were 2 in a million that any particular error could be attributable to the system.

Unsurprisingly the judge rejected this argument. If only 0.0002% of transactions were to go wrong then a typical day’s processing of eight million transactions would lead to 16 errors. It would be innumerate to look at one of those outcomes and argue that there was a 2 in a million chance of it being a system error. That probability would make sense only if one of the eight million were chosen at random. The supposed probability is irrelevant if you have chosen a case for investigation because you know it has a problem.

It seemed strange that the Post Office persisted with its flawed perspective. I knew all too well from my own experience of IT audit and testing that different systems, in different contexts, demanded different approaches to accuracy. For financial analysis and modelling it was counter-productive to chase 100% accuracy. It would be too difficult and time consuming. The pursuit might introduce such complexity and fragility to the system that it would fail to produce anything worthwhile, certainly in the timescales required. 98% accuracy might be good enough to give valuable answers to management, quickly enough for them to exploit them. Even 95% could be good enough in some cases.

In other contexts, when dealing with financial transactions and customers’ insurance policies you really do need a far higher level of accuracy. If you don’t reach 100% you need some way of spotting and handling the exceptions. These are not theoretical edge cases. They are people’s insurance policies or claims payments. Arguing that losing a tiny fraction of 1% is acceptable, would have been appallingly irresponsible, and I can’t put enough stress on the point that as IT auditors we would have come down hard, very hard, on anyone who tried to take that line. There are some things the system should always do, and some it should never do. Systems should never lose people’s data. They should never inadvertently produce apparently fraudulent transactions that could destroy small businesses and leave the owners destitute. The amounts at stake in each individual Horizon case were trivial as far as the Post Office was concerned, immaterial in accountancy jargon. But for individual sub-postmasters they were big enough to change, and to ruin, lives.

The willingness of the Post Office and Fujitsu to absolve the system of blame and accuse users instead was such a constant theme that it produced a three letter acronym I’d never seen before; UEB, or user error bias. Naturally this arose on the claimants’ side. The Post Office never accepted its validity, but it permeated their whole approach; Horizon was robust, therefore any discrepancies must be the fault of users, whether dishonestly or accidentally, and they could proceed safely on that basis. I knew from my experience that this was a dreadful mindset with which to approach fraud investigations. I will turn to this in my next post in this series.