NEW YORK (CBSNewYork/AP) -- The Secret Service says it is investigating a credit- and debit-card data theft at Target stores.
Secret Service spokesman Brian Leary confirms the agency is investigating, but declined to provide further details. It is customary for the Secret Service to investigate electronic crimes.
Reports began to surface Wednesday afternoon that hackers had gained access to card readers at hundreds of stores nationwide.
As CBS 2's Tracee Carrasco reported, the problem dates back as far as Black Friday, potentially compromising the personal data of millions of customers. Investigators believe hackers obtained data through software installed on machines that customers use to swipe magnetic strips on their cards, a source told CBS News.
There are no indications the breach impacts Target customers who shopped online.
Minneapolis-based Target Corp. did not respond to requests for comment.
An American Express spokeswoman released a statement saying the company "is aware of the incident, and we are working with Target. This is an ongoing investigation."
Paul Oster, a consumer credit expert, said hackers could have obtained addresses, dates of birth and social security numbers.
"So once they access that, it's very easy for them to open up other credit cards or gift cards," he said.
Oster recommends that anyone who has recently shopped at Target using a credit or debit card to enroll in a credit-monitoring program.
"Make sure, if you're going to use a company that has credit monitoring, they have the resolution service," he said. "So if you get alerted to a data breach, they can help you recover from that incident."
Experts also recommend that customers:
-- Check their statements for any unauthorized transactions
-- Change personal indentification number (PIN) for debit cards
-- Keep receipts in a safe place or dispose of them in a safe manner, such as shredding them.
Target has 1,797 stores in the U.S. and 124 in Canada.
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