About CVV2 and Credit Card Security
An important new security feature for online and other "card-not-present" transactions now appears on recently issued Visa, Mastercard, Discover, and American Express credit cards. This new feature, called CVV2, is a three-or four-digit value which provides a cryptographic check of the information embossed on the card. Note: CVV2 is now used at most major e-commerce websites, including Amazon.com. It protects the credit card holder from fraud.

Visa, Mastercard, and Discover:
The CVV2 three-digit value is printed on the signature panel on the back of your credit card immediately following the card account number.

American Express:
The CVV2 four-digit value is printed on the front of your credit card above and to the right of the card account number.

The CVV2 value helps validate two things:
The customer has an actual credit card in his/her possession.
The card account is legitimate.

CVV2 is only printed on your credit card - it is not contained in the magnetic stripe information, nor does it appear on sales receipts.