IRISH banks are to be closely monitored by the Data Protection Commissioner after it found AIB had committed a serious data protection breach.
AIB misreported missed loan repayments relating to about 12,000 of its customers to the Irish Credit Bureau, it emerged.
The error meant the customers' credit histories appeared worse or not as good as they should have been.
Instead of reporting the number of months overdue as required by The Credit Bureau, the bank reported the number of missed repayments.
The Office of the Data Protection Commissioner expressed disappointment it took AIB six weeks to resolve the error once it came to light.
The Commissioner now plans to check other financial institutions for the same problem.
AIB is investigating the impact of the error on a case-by-case basis.
It plans to see if affected customers had been put at a disadvantage when applying for new loans.
AIB has also promised to cover the €6 cost of a credit history report for each affected customer. AIB apologised for the error, which happened over a six-year period up to July 2012.
It was identified in May this year and reported to the Data Protection Commissioner by the bank.
Deputy Commissioner Gary Davis said AIB supplied inaccurate personal data to the ICB.
The data involved was part of a mass of information collected by the ICB about the loan repayment track records of millions of borrowers.
It is used by banks as a key factor in deciding whether or not to lend to customers.
In a statement, AIB said the error related to certain customers who were in arrears on loans to the bank.
AIB has written to the those affected and has offered to request a new copy of any affected customer's ICB statement.