If you've shopped at Target stores since Thanksgiving, your debit and credit card information may be in the hands of hackers.

"Approximately 40 million credit and debit card accounts may have been impacted between Nov. 27 and Dec. 15, 2013," Target said Thursday in a statement on its website.

The Secret Service confirmed thieves stole an unknown number of Target customers' payment information starting on Black Friday weekend.

Investigators believe the data stored in the cards' magnetic strips was hacked at the cash registers.

The breach reportedly involves Target stores nationwide. If you suspect any unauthorized activity, the company says to contact them at 866-852-8680.

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