Target Corp said data from about 40 million credit and debit cards might have been stolen from shoppers at its stores during the first three weeks of the holiday season, in the second-largest card breach at a U.S. retailer.
The data theft, unprecedented in its ferocity, took place over a 19-day period that began the day before Thanksgiving. Target said on Thursday that it identified and resolved the issue on December 15.
Though smaller than the breach disclosed in March 2007 by TJX Companies Inc, parent of apparel chains TJ Maxx and Marshalls, the data theft took place over a much shorter period and hit shoppers at the beginning of the U.S. holiday season.
Target said the breach might have compromised accounts between November 27 and December 15, a period of nearly three weeks.
The data theft revealed by TJX took place over 18 months, affecting 45.7 million payment cards, according to the company. Banks later said in court documents that the hackers could have obtained more than 94 million account numbers in the TJX case.
On Thursday, Target told customers in an alert on its website that the criminals had stolen customer names, payment card numbers, expiration dates and their CVV security codes.
Krebs on Security, a closely watched security industry blog that broke the news on Wednesday, said the breach involved nearly all of Target's 1,797 stores in the United States and investigators believed the data was obtained via software installed on point-of-sales terminals used to swipe magnetic strips on payment cards.
It is not yet clear how the attackers were able to compromise point-of-sales terminals at so many Target stores.
The U.S. Secret Service is working on the investigation, according to an agency spokeswoman.
Target's shares were down 1.9% an hour after the market opened to $62.33 U.S.
The shares have risen 7.4% this year, but have largely underperformed the broader S&P 500 index, which has risen 27% this year.
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