MINNEAPOLIS (TheBlaze/AP) — Millions of Target customers during the busiest shopping season of the year could be subject to credit card vulnerability after the store announced millions of accounts may have been exposed.

Target Data Breach

Target says that about 40 million credit and debit card accounts of customers may have been affected by a data breach that occurred at its U.S. stores between Nov. 27, 2013, and Dec. 15, 2013. (AP/Phil Coale)

The chain said 40 million customers who made purchases using credit and debit cards between Nov. 27 and Dec. 15 could be affected by the data breach.

The Minneapolis company said it immediately told authorities and financial institutions once it became aware of the breach and that it is teaming with a third-party forensics firm to investigate the matter. It said it is putting all “appropriate resources” toward the issue.

Target advised customers who suspect there has been unauthorized activity on their cards should call them at 866-852-8680.

The Secret Service also confirmed it was investigating the data breach.

“The Secret Service will confirm it is investigating the incident at Target,” spokesman Brian Leary told USA Today. “We don’t have any further comment because it’s an ongoing investigation.”

Watch WCBS-TV’s report about the breach:

Target is just the latest retailer to be hit with a data breach problem. TJX, which runs stores such as T.J. Maxx and Marshall’s, had a breach that began in July 2005 that exposed at least 45.7 million credit and debit cards to possible fraud. The breach wasn’t detected until December 2006. In June 2009 TJX agreed to pay $9.75 million in a settlement with multiple states related to the massive data theft but stressed at the time that it firmly believed it did not violate any consumer protection or data security laws.

“Target’s first priority is preserving the trust of our guests and we have moved swiftly to address this issue, so guests can shop with confidence. We regret any inconvenience this may cause,” Chairman, President and CEO Gregg Steinhafel said in a statement Thursday.

Target has 1,797 U.S. stores and 124 in Canada.

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