Credit card security code is the security code of credit card for online or telephone transactions. Generally, it is a 3-digit or 4-digit number printed on a credit card, and the printing position of different types of cards will be different.

Its generation method is that the bank extracts the account number, validity period and service code of the card, arranges them and then calculates them through a series of complicated algorithms. After this set of numbers is generated, only the issuing bank and the holder of the bank card know what this number is.

It is usually used to prove that the payer has a credit card at the time of transaction, thus preventing credit card fraud.

For example, the security code of UnionPay card is called CVN2, which has three digits and is printed on the back of the credit card after the last four digits of the card number.