Neiman Marcus this week apologized for a recent hack that resulted in stolen customer credit card data, and offered customers one year of free credit monitoring.

The retailer said that Social Security numbers and birth dates were not compromised "as best we know today," and the breach does not appear to have affected those who shopped online. Neiman does not use PIN pads in its stores, so PINs are safe.

Neiman first became aware of the problem in mid-December when "we were informed of potentially unauthorized payment card activity that occurred following customer purchases at our stores." The store hired a forensic investigator, who on Jan. 1 found evidence of a criminal cyber-security intrusion, and that investigation continues.

According to the New York Times, however, the intrusion dates back to July. The company acknowledged the breach after reporter Brian Krebs wrote about it.

"We deeply regret and are very sorry that some of our customers' payment cards were used fraudulently after making purchases at our stores," Karen Katz, president and CEO of the Neiman Marcus Group, said in a statement. "We have taken steps to notify those affected customers for whom we have contact information. We aim to protect your personal and financial information. We want you always to feel confident shopping at Neiman Marcus, and your trust in us is our absolute priority."

Neiman has disabled the malware it uncovered, she said, enhanced its security tools, and assessed and reinforced its related payment card systems. Still, Katz urged customers to watch their statements carefully and report any suspicious activity. Brands like Visa, MasterCard, American Express, Discover, and the Neiman Marcus card provide zero liability for those who had their numbers stolen.

Anyone who has made a payment card purchase at Neiman Marcus in the past year will get one year of free credit monitoring service. Details will be posted online by Friday, Jan. 24.

The Neiman hack comes after Target was also hit by hackers who compromised the accounts of upwards of 70 million shoppers. Target CEO Gregg Steinhafel told CNBC recently that the firm doesn't "know the full extent of what transpired, but what we do know is that there was malware installed on our point-of-sale registers. That much we've established."

Target and Neiman might not be the only ones hit by scammers. According to Reuters, three other retailers experienced similar incidents over the same time period.