Buyers beware as hackers have stolen credit card information for customers who shopped as recently as last month at 63 Barnes & Noble stores across the country, including stores in New York City, San Diego, Miami and Chicago, according to people briefed on the investigation. The company discovered that the information had been stolen but kept the matter quiet at the Justice Department's request so the F.B.I. could determine who was behind the attacks. Hackers stole the information by breaking into the keypads in front of registers where customers swipe their credit cards and enter their personal identification numbers, or PINs.

The attack was acknowledged by the company, saying that as a precaution customers who used their cards at any of the 63 Barnes & Noble where information was stolen should change their PINs and scan their accounts for unauthorized transactions. The activity had mainly occurred in September and had declined in recent weeks. But the company may have angered buyers by deciding not to tell its customers about the attack, saying that they had informed credit card companies that certain accounts might have been compromised.