The credit card security code is a set of 3 or 4 digits on the credit card. 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.

The security code of JCB card (Japan Credit Bureau) is called CAV2 (card authentication value 2), which has 3 digits and is printed on the back of the credit card number.

The security code of VISA card is called CVV2 (card verification value 2), which has 3 digits and is printed on the last 4 digits of the card number on the back of the credit card.

MarsterCard's security code is called CVC2 (Card Verification Code 2), which has 3 digits and is printed on the last 4 digits of the card number on the back of the credit card.

The security code of Discover card is called Cardmember ID, which has 3 digits and is printed on the signature column on the back of the credit card.

The security code of American Express is called CID (Card Identification Number), which has 4 digits and is printed on the front of the credit card above the credit card number.

The security code of China UnionPay is called CVN2 (card verification number 2), which has 3 digits and is printed after the 4 digits of the card number on the back of the credit card.