There wasn't just one bug, there were many. One of them was due to a "missing payments node", but there were many software faults, including rounding errors, da

There wasn't just one bug, there were many. One of them was due to a "missing payments node", but there were many software faults, including rounding errors, data corruption, and issues with synchronization between local and central databases. Two bugs are detailed here: https://www.theguardian.com/uk-news/2024/jan/09/how-the-post-offices-horizon-system-failed-a-technical-breakdown https://www.theguardian.com/uk-news/2024/jan/09/how-the-post... > One, named the “Dalmellington Bug”, after the village in Scotland where a post office operator first fell prey to it, would see the screen freeze as the user was attempting to confirm receipt of cash. Each time the user pressed “enter” on the frozen screen, it would silently update the record. In Dalmellington, that bug created a £24,000 discrepancy, which the Post Office tried to hold the post office operator responsible for. > Another bug, called the Callendar Square bug – again named after the first branch found to have been affected by it – created duplicate transactions due to an error in the database underpinning the system: despite being clear duplicates, the post office operator was again held responsible for the errors. There weren't just bugs, either Fujitsu had the ability of modifying or adding transactional records remotely, but always denied they had the ability to do so, as did the Post Office.