A computer security breach at the US parent of the TK Maxx discount clothing stores may have compromised the credit and debit card information of Irish shoppers.

In a statement released yesterday, the TJX Companies said it had "suffered an unauthorised intrusion into our computer systems that process and store information related to customer transactions".

The company has confirmed that the financial details of some US and Canadian customers have been stolen and it has contacted card issuers with the relevant information. TJX said it was "concerned" that the servers that process and store customer transactions for the TK Maxx shops in Ireland and Britain may also have been compromised, but the company's internal investigation has not been able to confirm this yet. TJX operates almost 200 TK Maxx stores in Ireland and Britain.

TJX has also established that some customers' driving licence numbers have been stolen and it has contacted these people. This raises the possibility that hackers could perpetrate identity theft by applying for credit cards and loans in the names of TJX customers without their knowledge.

The network breach took place in mid-December at TJX's corporate headquarters in Massachusetts. The compromised data relates to transactions in 2003 and from mid-May. "We have promptly alerted law enforcement authorities and an investigation is under way," TJX chairman Ben Cammarata said in a statement.

"We have also engaged two of the very best computer security experts to help us strengthen the security of our systems in order to prevent this from happening again and we believe customers should feel safe shopping in our stores," he added.

The external firms are understood to be IBM and security specialists General Dynamics. TJX said the containment plan was appropriate to prevent further breaches.

TK Maxx is advising customers to review their debit and credit card statements closely for any suspicious activity. Customers can also call a dedicated helpline on 0800-779015.