The last three digits are verification codes (also called "the last three digits"), which are the most useful and used for online transactions. The verification code of credit card is called CVV code. It is a series of 3-digit numbers generated by the card number, expiration date and service constraint code, and by the coding rules and encryption algorithm of the issuing bank.

According to bankers, the use of credit cards can be divided into "intra-card transactions" and "offline transactions". In the former, the cardholder swipes the card on the POS (sales terminal) of "physical stores" such as shopping malls and supermarkets, and signs the authorization to complete the transaction. Off-line transactions are common in hotels, airline sales centers and corporate finance. Similarly, through the POS system, you can provide the credit card account number and its verification code to complete the transaction.