A New England-based supermarket chain has warned of an information security breach that exposed an estimated 4.2 million credit card records.

Hannaford said hackers might have accessed customer credit and debit card numbers - but not the corresponding names or addresses - after hacking into systems involving card authorisation. Details on exactly how the breach happened are unclear, but the problem is reckoned to have extended from 7 December until its discovery earlier this month.

"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," Hannaford chief exec Ron Hodge said in an open letter to customers posted on the grocer's website.

The intrusion affected all 165 Hannaford stores, 106 Sweetbay stores in Florida, and some independently-owned retailers in New England that use Hannaford's payment systems.

Hannaford apologised for the snafu and offered to help field customer concerns through its information centre at 866-591-4580. It urged customers to keep a close eye on their credit card bills in case any unauthorised transactions appear.

The supermarket chain told the Boston Globe that the breach potentially exposed 4.2 million credit and debit card numbers. About 1,800 cases of fraud have being linked to the breach, the paper adds. The US Secret Service is investigating the attack.

Hannaford Bros is based in Maine, USA, but owned by Belgium's Delhaize Group.

The Hannaford's breach is extensive, but small potatoes compared to the estimated 45.7 million accounts compromised over a period of two years as a result of a customer data breach at retailer TJX, which runs T.J. Maxx and Marshalls retail chains. A badly secured wireless network at one of TJX's stores was blamed for the breach, the worst example in an increasing long list of customer data security breaches to date. ®

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