Hackers stole the bank card details of millions shoppers at bargain chain TK Maxx in what is thought to be the world's biggest credit card heist.
The crooks extracted at least 45.7 million credit and debit card numbers from the US- and UK-based computer systems of TJX, the US retailer that owns TK Maxx.
Banks and card companies have already found "preliminary evidence" of fraud using the data stolen from TJX, and police are investigating possible cases.
The numbers were accessed on the company's systems in Watford, England, and Framingham, Massachusetts, over a 17-month period and cover transactions dating as far back as December 2002.
The firm did not know how many of the cardholders affected were shoppers at TK Maxx's seven shops in Ireland, although more of them were likely to be American.
The case easily eclipses the largest single loss of consumer data previously reported, when just over 40 million Cardsystems Solutions records were compromised in 2005.
The FBI, Secret Service and state police agencies are investigating in America, where the company has around 2,000 TK Maxx, Marshalls, HomeGoods and AJ Wright stores.