A security breach that yielded Neiman Marcus customers' payment card information went undetected for nearly six months, according a report in the New York Times. The upscale department store revealed Friday that hackers may have stolen customers' credit and debit card information during an intrusion it detected in mid-December, but sources told the Times that the earliest time stamp on the breach was from July. During a call with credit card companies on Monday, the company acknowledged that the intrusion had been fully contained only a day earlier, three days after it was publicly revealed, sources told the newspaper. Neiman Marcus did not immediately respond to a CNET request for comment but told Reuters that it only learned of the breach last month. "We did not get our first alert that there might be something wrong until mid-December," Neiman Marcus spokesperson Ginger Reeder told Reuters. "We didn't find evidence until January 1."