You're about to use your credit card to purchase something over the Internet or the telephone and you're asked to provide the three or four numbers printed on the back of the card. Is it a valid question and is it safe to respond? It depends on who's asking. A merchant has a legitimate purpose for obtaining those numbers, but an ID thief can use them to commit fraud.

The numbers on the back of your credit card, often printed on the strip provided for your signature, are part of a new security code. The purpose is to verify that the person making a purchase online or over the phone — when the merchant cannot see the card — actually has the card in hand and is not someone else who simply knows the card number and expiration date.

"Unless a criminal already has your card or has previously copied these numbers from your card, there is no way to know the printed security code on the back," said Janet Kincaid, FDIC Senior Consumer Affairs Officer. "That is why it is especially important to safeguard the information."

Her suggestions: Try to be sure you are dealing with a legitimate Web site when providing credit card information online. Also, look for a logo of a padlock or other indication that card numbers are protected during Internet transmissions. In addition, only provide your credit card information when you originate a transaction, not in response to an unsolicited call or e-mail, which may be fraudulent. For more information about using and protecting the security code on your credit card, contact your card issuer.