Bank of Ireland has had four company laptops stolen, containing around 10,000 customer details.
The bank confirmed that four laptop computers - containing information on customers' names and addresses, medical backgrounds, life assurance details and bank account details - were stolen between June and October of last year. The data held was not encrypted.
The laptops contained information relating to some customers who either obtained a quote or took out a life assurance policy. It is believed three were stolen from cars from sales managers, and one from a bank branch. The breach affected branches in Drogheda, Dunleer, Bagnelstown, Stephen's Green, Tallaght, Montrose and Court Place in Carlow.
A spokesperson declined to comment on the ongoing investigation into recovering the lost information or engaging third parties into a review.
"We are conducting a review of what happened and looking at what will happen in the future," she said.
Although the computers were stolen last year, Ireland's data protection commissioner was only informed of the breach on Friday. The commissioner has begun an inquiry.
In a statement, the commissioner said: "A more detailed report has been sought from Bank of Ireland into the exact circumstances surrounding the loss of the personal data.
"The investigation will focus on the justification for the personal data, including sensitive medical data in some cases, being placed on the laptops in the first place, the security arrangements in place and the exact circumstances which led to the delay in the reporting of this matter internally within the Bank of Ireland to the appropriate personnel for the taking of further action.
"Consideration will then be given as to what further action will be sought from Bank of Ireland to ensure that the obligations contained in the Data Protection Acts in this area are met."
The bank spokesperson said the bank has plans to start rolling out encryption for its laptops in May.
"In the unlikely event that any customers lose money following the laptop thefts, they will be reimbursed," the spokesperson said.