Bank of Ireland has been fined €750,000 by the Data Protection Commission (DPC) following an investigation into 10 data breaches involving the bank's Banking 365 system.
The issue saw users of the online banking platform being given access to accounts other than their own.
The problem affected 136 accounts but no financial loss has been identified for the customers impacted.
In six of the ten data breaches, unauthorised people gained access to customers' accounts online as a result of staff not following bank procedures correctly.
The remaining four data breaches were as a result of a flaw in the bank's customer information system.
Bank of Ireland was made aware of a number of cases where customers who logged into their unique account through the Banking 365 portal could view the account transaction details of third parties.
Bank of Ireland said it sincerely apologised for the errors.
"We take very seriously our regulatory and compliance obligations - and our duty to customers - and we acknowledge that we fell short in this instance," the bank said in a statement.
"The bank has rectified the IT issue which caused some of the errors. We have also introduced additional quality assurance checks, conducted enhanced training for staff to address manual errors, and centralised a number of teams in order to improve data management and oversight," Bank of Ireland said.
In April 2022, Bank of Ireland was fined €463,000 by the Data Protection Commission for data breaches affecting more than 50,000 customers.
