The security code of a credit card is the three digits or the last three digits of a series of digits on the signature strip on the back of an ordinary credit card. Mainly used for online transactions or other occasions where cards cannot be verified immediately.

The serial cards issued by VISA organization are called CVV2 code, and MasterCard organization is CVC2 code. The names are different, but the generating principle of them is the same. According to the requirements of VISA and MasterCard organizations, online websites are not allowed to save CVC or CVV codes during the transaction. Online transactions are risky and require the cardholder's own attention.