CARD VERIFICATION VALUE 2 code (CVV2) is a free fraud control tool. In fact, in most cases, it is the ONLY fraud control tool which does not carry a per use add fee.
Remember that CVV2 CANNOT be stored!
CVV2 code is 3 digit code on back of Visa / MasterCard / Discover cards and 4 digit code on front of American Express cards (http://en.wikipedia.org/wiki/CVV2)
