The Card Verification Value 2 (CVV2) code provides customers with added credit card transaction security. The CVV2 code requires physical access to the credit card thus reducing the risk of Internet credit card fraud.
Visa, MasterCard & Discover:
This number is printed on your MasterCard, Visa or Discover card in the signature area on the back of the card. (it is the last 3 digits AFTER the credit card number in the signature area of the card).
American Express:
This number is printed on the front of your American Express above the number, to the right of the card. (should be 4 digits long).