Irish banks AIB and Permanent TSB say that they suspect that some of their customers have fallen victim to card fraud after a massive data breach at loyalty points outfit Loyaltybuild.
Loyaltybuild was hit by hackers last month, with crooks making off with the full card details of at least 376,000 customers, says the Office of the Data Protection Commissioner (ODPC).
Data Protection Commissioner Billy Hawkes says that the card data - including CVV numbers - were stored in unencrypted form.
An AIB spokeswoman told the Irish Times that the bank has been inundated with calls from worried customers and that a trawl of its systems has found signs of fraud on some cards, although these can not be directly linked to the Loyaltybuild hack.
Permanent TSB has also confirmed "some indications" of fraud on some cards but is not yet drawing a direct line with Loyaltybuild.
The Irish Payment Services Organisation has moved to calm fears, saying that most of the cards affected will now be expired or have been replaced, and so are of no use to thieves.
"IPSO advises that cardholders should not be concerned regarding their accounts as they will not be liable for any fraud that has occurred as a result of this incident," says a statement.