Neiman Marcus, which operates more than 40 upscale stores and clearance stores, is working with the Secret Service on the breach. Joe Raedle/Getty Images

Luxury merchant Neiman Marcus confirmed Saturday that thieves stole some of its customers' payment card information and made unauthorized charges over the holiday season, becoming the second retailer in recent weeks to announce it had fallen victim to a cyber-security attack.

The hacking, announced weeks after Target revealed its own breach, underscores the increasing challenges merchants face in protecting consumer information.

Ginger Reeder, spokeswoman for Dallas-based Neiman Marcus Group Ltd., said in an email Saturday that the retailer had been notified in mid-December by its credit card processor about potentially unauthorized payment activity following customer purchases at stores.

On Jan. 1, a forensics firm confirmed evidence that the upscale retailer was a victim of a criminal cyber-security intrusion and that some customers' credit and debit cards were possibly compromised as a result.

Reeder wouldn't estimate how many customers may have been affected, but said the merchant is notifying customers whose cards it now knows were used fraudulently.

Neiman Marcus, which operates more than 40 upscale stores and clearance stores, is working with the Secret Service on the breach, she said.

"We have begun to contain the intrusion and have taken significant steps to further enhance information security," Reeder wrote.