To be precise, it is CVV, which is a security code.

gt; CVV password verification means that commercial banks add custom algorithm verification codes to the bank card number encoding rules and magnetic stripe data formats they use. The relevant bank cards are also called CVN bank cards. .

CVV information is stored in the magnetic track of the magnetic stripe bank card. Based on the card number, track master account number, card-issuing bank logo code and other information, it is encrypted through a special encryption algorithm customized by each bank. Each step uses CVKA technology encrypts and gets the verification code. Since the encryption algorithms of different banks are different, some counterfeit cards illegally produced using the obtained bank card information can be identified and cannot be used when the card issuer decrypts them.