CVV2 is a new authentication scheme established by credit card companies to further efforts towards reducing fraud for internet transactions. It consists of requiring a card holder to enter the CVV2 number in at transaction time to verify that the card is on hand. VISA & MasterCard
This number is printed on your MasterCard & Visa cards in the signature area of 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
American Express cards show the cvv2 printed above and to the right of the imprinted card number on the front of the card.