Hackers have stolen 4.2 million credit and debit card details from a US supermarket chain by swiping the data during payment authorisation transmissions in stores.
The theft took place at the Hannaford Brothers and Sweetbay outlets in the eastern US.
"The stolen data was limited to credit and debit card numbers and expiration dates, and was illegally accessed from our computer systems during transmission of card authorisation," said Hannaford chief executive Ron Hodge on the company website.
Hannaford is reported to have become aware of the theft at the end of February, but it is believed the data could have been stolen as far back as last December.
Although only credit card numbers and expiration dates were stolen, not the associated names and addresses, as many as 1,800 fraud incidents have been linked to the theft.
The world's largest hack of credit card numbers was at the TJX group of companies in 2005, which affected 94 million card holders.