The UK Post Office has admitted that dodgy software has wrongly prosecuted staff for theft and forced some to pay back money they did not take.
More than 100 say they were wrongly prosecuted or made to repay money after computers made non-existent shortfalls. Some have lost their homes and others jailed because of the software cock-up.
The Post Office claimed that an internal report showed its system was effective but admitted that better training and support was needed.
That is not what independent investigators Second Sight, who were employed by the Post Office, said when they looked at the software.
According to the BBC, Second Sight said that although there was no evidence of systemic problems with the core software, it did have bugs.
One of these occasions resulted in shortfalls of up to £9,000 at 76 branches. In this case, at least, the Post Office later made good those losses and the sub-postmasters were not held liable.
But in other situations that has not been the case and the problem has mostly been with sub-postmasters, who run the smaller post offices in the UK, and are not directly employed by the Post Office.
They have to balance their books using the Post Office's Horizon computer system which processes all transactions.
Sub-postmasters have claimed for years that they have been wrongly accused of theft after their computers notified them of shortages that sometimes amounted to tens of thousands of pounds.
They had to pay in the missing amounts themselves, lost their contracts and in some cases went to jail.
Second Sight said the Post Office's initial investigation failed at first to identify the root cause of the problems. It said that more help should have been given to sub-postmasters, who had no way of defending themselves.
Now some of them are thinking of suing.
One nightmare case happened to Jo Hamilton, who used to run a sub-post office from her village shop in South Warnborough.
In 2005 she got to the end of a week and was £2,000 short so she rang the helpdesk and they told her to do various things before claiming she was £4,000 short.
They then said that she had to pay £4,000 because her contract said she would make good any losses. However, while she was doing that, the figure jumped up to £9,000.
The shortfalls kept getting higher and by the time the figure reached £36,000, she lied to the Post Office, wrongly telling them the books were balancing just so that she could open the office the next day.
She ended up pleading guilty to false accounting.
The Post Office has proposed setting up a working group to investigate further.