WASHINGTON — 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 around Sept. 14 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, according to these people.

The information was stolen by hackers who broke into the keypads in front of registers where customers swipe their credit cards and enter their personal identification numbers, or PINs.

In response to questions about the attack, the company acknowledged the security breach, 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.