AIB is to refund more than €8 million to users of its cash machines after anti-fraud measures led to customers’ accounts being debited even when the withdrawal was unsuccessful.

In a statement, AIB confirmed it would refund more than €8 million to people who had used its cash machines between 2003 and 2010 but left their money behind.

Some €5.1 million has been earmarked for 41,000 transactions involving AIB customers while €3.2 million has been set aside to compensate 30,000 non-AIB customers.

The automatic repayments will include interest and affected cardholders will be contacted by their banks over the coming days to inform them of the refund, which, the bank said, would average €116 per transaction.

The bank said the problem had arisen following the introduction of anti-fraud measures in the 1990s which were aimed at stopping the automatic processing of refunds if money was returned to an ATM after not being collected by a user within a 30-second time limit.

Like all Ireland's main retail banks, AIB introduced the security measures to stop scammers who were using compromised cards to withdraw substantial sums of money. When the money came out of the machine, the scammer removed the top and bottom notes in the pile. These two notes were retracted by the machine, which would wrongly record that no money had been withdrawn.

AIB was ordered to carry out its ATM audit by the Financial Regulator last summer after the Bank of Ireland announced the flaw in the system and reported that it was issuing €3 million in refunds to 43,000 customers who made withdrawals between 2005 and 2009 but never took their money.

Bank of Ireland also published research suggesting that among the most common reasons people forgot to take their money were incoming mobile phone calls and other distractions and a failure to take back the debit card, which must be withdrawn in order for the money to appear was also cited.

A spokesman for AIB told The Irish Times that when the bank introduced the new measures, it had been assumed that anyone who left their money behind at an ATM would contact their bank to explain their mistake. He accepted that the assumption had been wrong and substantial numbers of affected people never contacted their banks.

He said changes had now been put in place to prevent a reoccurrence.

There were 57 million ATM transactions from AIB machines last year with the total value of withdrawals standing at around €7.7 billion.