A credit card verification number is a three or four digit number that appears on a credit or debit card and is never embossed. The verification number is generated when the card is issued by the financial institution. It is an important anti-fraud security feature for transactions where the physical card is not presented to the merchant, such as transactions over the Internet or the phone.
Discover, MasterCard and Visa
On Discover, MasterCard and Visa debit and credit cards, the three-digit security code is located on the back of the card. Sometimes the back of the card will carry the cardholders 16-digit account number followed the three digit security code; otherwise, cardholders can find the last four digits of their account number followed by the three digit security code.
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On American Express cards, the security code is a four digit number that appears on the front right hand side of the card and is not embossed.
After a given transaction has been processed, the merchant is required to discard the security number. The security code does not appear on receipts or on any of the cardholder's statements.
By using the security code in transactions where the physical card is not presented at the time of the transaction, the merchant can be assured that the user of the card did not obtain a card number from a discarded receipt or other illegitimate source.
Other names of the security code include: card security code, or CSC; card validation value, or CVV, for Visa cards; card validation code, or CVC, for MasterCard cards; and card identification, or CID, for American Express and Discover cards.