Post Office Horizon Scandal - Computerphile

Computer bugs were found to be the reason many sub-postmasters and sub-postmistresses were wrongly convicted of stealing and false accounting. Professor Steven Murdoch, a professor of Security Engineering and a Royal Society University Research Fellow at UCL explains the sorts of faults that were found.


This video was filmed and edited by Sean Riley.

[nutsnproud]

Our local sub-postmaster used to print out a duplicate receipt for every transaction even somebody wanting a stamp and keep a copy. Post Office once said he was short and had the duplicate paper receipts to prove he wasn't. It cost him a lot of money for the extra paper rolls and ink cartridges but he said it was worth it.

[AfterTheSingularity]

I followed this case in Private Eye over the years, and it was clear from the start that the Post Office knew it was more than a coincidence that so many postmasters were coming up short, but it seemed that they just didn't want to lose face by admitting there was an error, so carried on prosecuting and prosecuting. Absolutely scandalous.

[Alorand]

One of the worst things in life is being accused of something that you didn't do.
I can't imagine how horrible it must feel to go to jail over a software glitch...

[audiodoctor]

2 years ago this video came out and only now is it being heard.

[steves]

I’ve worked in IT for 40 years dealing with various banking, payroll and other finance systems. One of the big things I’ve learnt is that with any complex system that no matter how much you test any error should be assumed to be in the system and not fraud. Of course fraud happens but before you start prosecuting anyone you better be really certain that it is not a system issue.

[TonyJewell]

This was an absolute scandal and ruined people's lives. The power the post office had under an ancient law to privately interview the accused in police stations supposedly under caution and hide other cases from them was egregious and compounded the problem.

My heart goes out to the victims who have suffered from these baseless accusations. I recommend all SW engineers and system designers listen to the BBC and guardian podcasts on the subject to appreciate how important it is to get these things right and show true due diligence in their profession. Don't be afraid to call out issues you might see in any systems you work on.

Anthony (semi-retired SW engineer).

[themagpieable]

This whole story warrants a lot more conversation in the software industry. Going forward it should be required reading alongside the Therac-25 scandal. It also demonstrates the issues with blindly trusting computer programs without any compassion for real people. The many stories of those who were prosecuted, fined, jailed, some of them dying before their verdicts were overturned, are heartbreaking.

The real scandal is that the court automatically assumed that the digital data presented is correct and trustworthy.
That is the main topic of our times: Are our digital systems trustworthy enough to count as evidence in court?
Perhaps Computerphile should invite Ross Anderson again for some basic security engineering lessons. ;)

[eliotcougar]

Our local supermarket is infamous for sending all their cashiers to jail… They claim that they all steal money… First they fine them for inconsistencies in data on their terminal, then if "theft" continues they call the police… They've sent maybe a dozen people to jail... Their system often doesn't work... Sometimes you need to retry paying with a bank card several times for the payment to go through... Sometimes the payment goes through, but the receipt printer hangs... Sometimes their system can't find the product ID when they scan the barcode... The cashiers are instructed to unplug their terminal from the mains, and plug it back...

I wonder if all those cashiers were indeed innocent...

[Richardincancale]

It’s a disgraceful story. Distributed transaction processing with two-phase commit was sorted and implemented in the mid-1980s. If systems today are failing the ACID test it’s due to incompetence by the system designers.

[chris]

I’ve had a problem similar to this before, a meal payment transaction system would charge you without checking to see if the order had actually been successfully received. Bad code does show up often in the world.

[TomWhi]

I’m on episode 3 of the itv drama and needed a break because it (I) was getting a bit emotional, came to YouTube and this was the first video in my recommendations. This is a great explanation from the tech point of view! Now I just need to find the strength to finish the drama!

[tjoebtjoeb]

I once ordered at Burger King through these touch screens. Right at the point of paying, the system froze and did a reboot. No receipt printed, no order placed, but money withdrawn from my account... What a struggle that was to explain.. 🤦‍♂️ Bad code is out there, even at big companies..

[kendalljenkins]

Any company or government entity in this situation would have immediately sued a multi billion dollar corporation like Fujitsu for screwing this up so royally. The fact that the Post Office hasn't even hinted at doing that, makes me think there were some major kickbacks to some post office people when the contract was rewarded to Fujitsu, and they want to avoid that being discovered. It would also explain the ridiculous lengths that the post office went to in order to blame the local post masters, when it was extremely obvious to anyone with one brain cell that the Fujitsu system was a flawed mess

[gazzmilsom]

This is a wonderfully calm explanation of the technical failures behind an absolutely outrageous scandal.

[NickNorton]

Closed source, poorly audited, faceless unaccountable/uncontactable software devs.
Execution by Software rather than Executable Software.

[vinny]

These kinds of bugs are remarkably easy to get. I had to fix a bug in a client's webshop that would sporadically get way more stock in thewebshop than they actually had. Turns out there was some sort of denial of service-ish thing where robots where trying to reserve as many items as they could. But ofcourse if you never actually purchase then the system will remove your shoppingcart and return the items to stock. Turns out that if people where reserving items while it was getting returned to stock the deleting of the cart would fail and a little later the same cart would be deleted again and presto; more stock than you started with.

That disappeared when I implemented transactions. And yes I notified the author of the shop and basically told him to go and learn how databases work.

[AmySoyka]

So grateful that this has been explained in technical detail.

Did anyone else get hung up watching the drama when the guy from Bridlington in the first episode notices the discrepancy in the EFTPOS terminal printouts ~ but then doesn't bring it up with the Auditor in episode two?

[BlackHoleForge]

I am pleasantly surprised by how many times I enjoy watching videos of the British postal system. Thanks to Tom Scott for introducing me.

[TheDaftySage]

Unbelievable. A second year CS student would know how to consider these problems.