More than €600,000 was inadvertently paid in welfare to people who were behind bars over the past two years.
The Department of Social Protection said they had uncovered 735 separate payments to criminals that should not have been made.
There were a total of €303,000 in overpayments last year of which around €160,000 has already been recovered.
In 2023, just under €304,000 was paid to people behind bars with nearly €228,000 – or around three quarters of the total – recouped for the taxpayer.
The Department said that 368 overpayments had been flagged last year relating to 355 individuals, with some people entitled to more than one payment.
For 2023, there were 367 overpayments to 359 people who had been sent to jail.
The Department said recovery of the money can be an ongoing process depending on how the overpayment will be repaid.
They said that when a person was in prison, the department suspended or stopped any social welfare payment to which they were not entitled.
They said they were provided weekly data by the Irish Prison Service on who new arrivals into their custody.
This was matched against the Department’s own data on welfare payments for “the prevention, detection and deterrence of fraud.”
Most payments were stopped quickly and might only continue to be made for a very short period of time.
Asked about the overpayments, a spokesman for the Department of Social Protection said: “In a small number of cases overpayments may arise due to the time lag between receiving information from the Irish Prison Service and stopping the payment”.
“People who have been overpaid social welfare have a liability to refund the overpayment as they have been in receipt of a payment to which they were not entitled,” he added.
Reporting by Ken Foxe
