Target says information from up to 40 million credit and debit card accounts belonging to their customers may have been stolen.
Target says the breach may have occurred between Nov. 27 and Dec. 15.
Target says once it learned of the breach, it immediately told authorities and financial institutions and is teaming with a third-party forensics firm to investigate.
Target Corp. said that customers who made purchases at its U.S. stores during the impacted period and suspected unauthorized activity should call them at 866-852-8680.
Target has 1,797 U.S. stores and 124 in Canada.