NEW YORK — With less than a week until Christmas, thieves have stolen the credit- and debit-card information of about 40 million Target shoppers. Target says accounts may have been exposed for anyone who made purchases by swiping cards at terminals in its U.S. stores between Nov. 27 and Dec. 15. The stolen information includes customer names, credit- and debit-card numbers, card-expiration dates and the three-digit security codes on the backs of cards. The stolen information included Target store- brand cards and major card brands such as Visa and MasterCard.

The data breach did not affect online purchases, the company said.

Here are some answers to the most common questions about the theft:

Q: I shopped at Target during that time. What should I do?

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A: Check your credit-card statements carefully. If you see suspicious charges, report the activity to your credit-card companies and call Target at 866-852-8680. You can report cases of identity theft to law enforcement or the Federal Trade Commission (FTC).

You can get more information about identity theft on the FTC’s website at www.consumer.gov/idtheft, or by calling the FTC at 877-438-4338.

Q: How did the breach occur?

A: Target isn’t saying.

Q: Who pays if there are fraudulent charges on my account?

A: The good news is in most cases consumers aren’t on the hook for fraudulent charges. Credit-card companies are often able to flag the charges before they go through and shut down your card. If that doesn’t happen, the card issuer will generally strip charges you claim are fraudulent off your card immediately. Because the fraud has been tied to Target, it will be the retailer that ultimately compensates the banks and credit-card companies.

Q: How can I protect myself?

A: Cash is king. You can only lose what you’re carrying, though many people may not feel safe walking around with a wad of bills.

It’s worth noting that while debit cards offer many of the same perks as credit cards, they often don’t come with the same kind of fraud protections. As a result, those card holders may have a tougher time getting their money back if their number is stolen.

Q: Can the bad guys be caught?

A: Ken Stasiak, founder and chief executive of Secure State, says that given the sophistication of this attack, there’s only about a 5 percent chance that the perpetrators will eventually be caught and prosecuted.

Q: Why is the Secret Service investigating?

A: While it’s most famous for protecting the president, the Secret Service also is responsible for protecting the nation’s financial infrastructure and payment systems. As a result, it has broad jurisdiction over a wide variety of financial crimes. It isn’t uncommon for the agency to investigate major thefts involving credit-card information.