DENVER -- Just when you thought you'd done everything possible to protect your credit and your credit cards, someone's come up with still another way to scam you. And this latest scam is particularly evil because you think you're getting help, Consumer Champ Bill Clarke said.

The scam starts with a phone call from someone who says you're in trouble because someone has been using your credit card.

"They call up and offer to help and they scare you, and it sounds very official," said Susan Liehe of the Denver Better Business Bureau.

The person on the other line claims to be with Visa or Mastercard, and claims he works with the credit card's security and fraud department.

"(He'll say), 'Here's the case number. Here's my badge number. I'm the fraud investigation officer,'" Liehe said.

The scammer then warns you that someone has made unauthorized charges to your account. He or she claims to already have the numbers on the front of your credit card but he needs you to look on the back of the card to give him the last three numbers -- sometimes called the security code --to verify that you have the card.

"You provide them and then the bad guy on the other end says, 'Yes, that's correct.' As if you're being checked up on," Liehe said.

Those three little numbers mean he can use your card anywhere.

"You need to think of ID theft as a jigsaw puzzle. And (the last three digits) represent the last little piece that the bandit needs to complete the picture," Liehe said.

Officials say never give any of your personal information to someone who calls you. Real credit companies will never ask for anything on the card, unless you call them to make changes to your account.

In the case of this particular scam, the caller says, "If you have any questions, here's the toll-free number to call." The phone number will be legitimate but by the time one victim called, the scam artist had racked up almost $500 in charges to the victim's account.

This new twist in the ID theft has been reported in Louisville, Kent., and Vancouver, British Columbia. Visa and Mastercard confirmed to a BBB official that this scam is also being used in the Midwest.

The scam is an example of what the Federal Trade Commission calls "pretexting." That is, someone calls you and pretends to be someone they are not. They call under the pretense that they are "the bank" or "the police" or "the credit card issuer." They pretend to be on your side and to help you fix a problem when they are the problem, the FTC says.

This is an account of what happened to one victim in Kentucky.

The scam artist calls and says:

"This is Carl Patterson and I'm calling from the security and fraud department at VISA. My badge number is 12460. Your card has been flagged for an unusual purchase pattern, and I'm calling to verify. Did you purchase an anti-telemarketing device for $497.99 from a marketing company based in Arizona?"
When you say "No," the caller continues with, "Then we will be issuing a credit to your account. This is a company we have been watching and the charges range from $297 to $497, just under the $500 purchase pattern that flags most cards. Before your next statement, the credit will be sent to (gives you your address), is that correct?" You say, "Yes."
The caller continues, "I will be starting a fraud investigation. If you have any questions, you should call the 800 number listed on your card -- 1-800-VISA -- and ask for security. You will need to refer to this control number."

Then he gives you a six digit number. "Do you need me to read it again?" the caller asks.
The caller then says he "needs to verify you are in possession of your card. Turn the card over. There are seven numbers; first four are 1234 (whatever) the next three are the security numbers that verify you are in possession of the card. These are the numbers you use to make Internet purchases to prove you have the card. Read me the last three numbers."
When you do, he says, "That is correct. I just needed to verify that the card has not been lost or stolen, and that you still have your card. Do you have any other questions? Don't hesitate to call back if you do."
You actually say very little, and they never ask for or tell you the card number.