CVV2 is a security measure for credit cards. Since a CVV2 number is listed on your credit card, but is not stored anywhere, the only way to know the correct CVV2 number for your credit card is to physically have possession of the card itself. All VISA, Discover, MasterCard and American Express cards made in America in the past 5 years or so have a CVV2 number. However Diners Club does not use a security code.
How to find your CVV2 number:
On a VISA, Discover or MasterCard, please turn your card over and look in the signature strip. You will find (either the entire 16-digit string of your card number, OR just the last 4 digits), followed by a space, followed by a 3-digit number. That 3-digit number is your CVV2 number.(See below)
VISA, Discover & MasterCard
On American Express Cards, the CVV2 number is a 4-digit number that appears above the end of your card number. (See below)