The last three digits of the signature column on the back of the credit card are CVV2 code, also called credit card security code, which is the security code of credit card transaction. Generally printed on the back of the credit card after the signature, that is, the last 3 digits in italics; It is used to prove that the payer has a credit card at the time of transaction, thus preventing credit card fraud. The CVV2 code is equivalent to the ID card of a credit card, and the cardholder can use this code for consumer transactions. It is understood that overseas website shopping does not require a password, as long as the buyer provides the account number and security code, the transaction can be completed; There are also merchants in China who have signed contracts with banks, and do online or telephone transactions without passwords. Only anti-counterfeiting codes can complete remittance.