Conclusion: The three-digit number on the back of a credit card, often called a CVV2 code or a similar security code, is information unique to the issuing bank and cardholder and cannot be queried through the bank system. The three-digit generation process involves the card account number, validity period and service code, and is encrypted by a complex algorithm. Although it is as important as a password, because some websites only require this information for payment, it is easily overlooked, so be sure to keep it carefully to avoid leaking it.

The following is a detailed description of the security code types of different credit card brands:

-China Merchants Bank’s credit card: the security code is the three-digit number located in the signature column on the back of the card, the last three of the card number. Bit.

-UnionPay Card (ChinaUnionPay): The security code is called CVN2 and is located after the last four digits of the card number in the signature field.

-MasterCard: The security code is CVC2, also in the last four digits of the card number in the signature field.

-DiscoverCard: The security code is CardmemberID, located on the signature column.

-American Express: The security code is CID, located above the credit card number on the front.

-JCB Card (Japan Credit Bureau): The security code is CAV2, which is also the last three digits of the card number in the signature column.

In general, understanding and properly protecting these security codes is an important part of ensuring credit card security. Remember, never reveal these three crucial numbers, no matter what the circumstances.