Security number on American Express credit cards
The purpose of the credit card security number is to prevent thieves from using your credit card number with internet and telephone merchants who cannot physically compare the signatures on your card with the purchaser signature. The security number is a relatively new internet fraud protection mechanism, and many people are unfamiliar with it.
The security number is a random number added to the card by American Express. When our credit card processing company - 2Checkout.com communicates with American Express to get authorization to charge your credit card, 2Checkout.com also sends the security number that was provided. American Express looks to see if your account has enough available credit, and they also look to see that the security number provided matches what they printed onto your credit card. When you get a one-time-use card number for use on the internet, use the real security number on your American Express card; that is what they are expecting.
If the security number does not match, it is a reasonable assumption that the person using your credit card is not you, and although there might be enough available credit to handle the purchase, it would be unwise for us to process the purchase. If it were you making the purchase, you would know the proper security number. A thief would not.
If you have multiple credit cards, it is best if you designate one credit card just for internet purchases, so that no one but you ever sees the security number. Stores such as Ask The Meatman that verify the security number prevent thieves from pretending to be you.