To add the Fujitsu Tech Support had remote access to the postmaster accounts and were able to change the takings without the knowledge or consent of the postmaster. This was denied for years.I think....if i recall correctly.
New accounting system introduced.
The system is basically rubbish, with accounting errors.
Post masters get blamed for stealing.
Post Office prosecuted them (I did not know they had powers...I thought it was only the CPS).
They were forced to admit guilt, pay back money wrongly accused or go to prison.
All because the system was wrong and nobody questioned the programming, or at least, those that did, had no powers.
The TV show was compelling viewing and it has a 5th part that is an actual documentary of the real life people involved in the whole thing.