What Is a CSC Code?

Card Not Present Transactions

• Merchants typically request the CSC of a credit card as an additional security measure for "card not present" transactions conducted online, or by telephone, fax or mail order. In many countries, cardholders must supply the CSC as protection against credit card fraud for both the buyer and the seller, for any transaction where they are not present in person. By contrast, the card validation code (CVC) is used only for transactions where cardholders are present in person.

How a CSC Works

• When a credit card holder performs a transaction, such as an Internet purchase, the merchant concerned submits the CSC to the cardholder's credit card provider and receives a response depending on whether or not the CSC matches the number on file with the provider. If merchants receive a positive response they accept an order, but if they receive a negative response they reject it. It is possible the CSC matches the number on file, but the address details do not match -- if the cardholder has recently moved, or if a fraudster is attempting a purchase -- in which case the merchant will request clarification from the cardholder.

Location

• The length of a CSC and its location on a credit card varies according to the credit card provider. On Discover, MasterCard and Visa credit cards, for example, the CSC appears as a three-digit number printed on the extreme right of the signature panel on the back of the card. On American Express credit cards, on the other hand, the CSC appears as a four-digit number printed on the front of the card above the card number.

CVC2 versus CVC

• The CSC, otherwise known as the card validation code 2 (CVC2), should not be confused with another security measure, known as card validation code (CVC). The value of the CSC is generated when a credit card is issued, by encoding, or encrypting, the card number and the expiration date, and although the CSC is printed on the card, it is not encoded onto the magnetic strip. The value of the CVC, on the other hand, is encoded onto the magnetic strip to protect its integrity and reveal any alteration or counterfeiting.