More than 60,000 Supervalu customers may have had their payment card details compromised.
It emerged last night that a security breach, involving the retailer's Getaway Breaks loyalty programme, is more serious than initially thought.
On November 4, Supervalu reported to the Data Protection Commissioner that the system through which its loyalty programme customers book short breaks had been compromised.
The supermarket now believes there is a high risk that a third party accessed the payment card details of up to 62,500 customers who made Getaway Break bookings between January 2011 and February 2012.
It is advising anyone who made a booking during this period to contact their bank and check for suspicious activity on their cards.
Supervalu says it has suspended the Getaway Breaks booking system pending a thorough investigation.
It says the problem is confined to customers who booked holidays on the Getaway Breaks loyalty programme, and not to any other customers of Supervalu.
The retailer is also advising customers to treat with extreme caution any unsolicited communication they received in relation to Supervalu Getaway Breaks.