Neiman Marcus Group said it was told by its credit-card processor in mid-December that some unauthorized purchases may have been made with customer cards, the second retailer after Target Corp. to be struck recently by hackers.

"We informed federal law enforcement agencies and are working actively with the U.S. Secret Service, the payment brands, our credit card processor, a leading investigations, intelligence and risk management firm, and a leading forensics firm to investigate the situation," Ginger Reeder, vice president of corporate communications, said in an e-mail.

Reeder declined to name the card processor, the investigations firm or the forensic firm. Some cards may have been "compromised," she said, adding that the company has taken steps to enhance information security.

The cyberattack on Dallas-based Neiman Marcus was first reported Friday by the Wall Street Journal.