Neiman Marcus on Thursday disclosed details of a data breach it suffered over a three-month period last year that resulted in the theft of 1.1 million customers' debit and credit cards. The attackers hacked into the high-end retailer's computer systems and planted malware that siphoned customer card information during transactions.

There is no indication thus far that customers who shopped online with Neiman Marcus were exposed in the hack, nor were customers' social security numbers and birth dates, Neiman Marcus Group president and CEO Karen Katz said in a letter on the retailer's website. Neiman Marcus and Bergdorf Goodman payment card accounts have not been seen being used fraudulently, she said.

"We deeply regret and are very sorry that some of our customers' payment cards were used fraudulently after making purchases at our stores. We have taken steps to notify those affected customers for whom we have contact information. We aim to protect your personal and financial information," Katz said.

PINs were not exposed because the retailer doesn't use PIN pads in its stores, according to the retailer.

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