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.

When the general public apply for credit cards, the General Application Form for Credit Cards (Personal Cards) provided by the Credit Card Center and the attached Master Contract for Credit Cards (Personal Cards) do not contain any introductory or warning words about CVV codes. Most cardholders' first contact with CVV code occurs in the actual operation of online payment-"Please enter the last three digits of the credit card number to verify your identity". But not many cardholders realize that they are using another "password", which also needs protection. Therefore, after receiving a new credit card, you should remember your CVV code and immediately cross it off the card to prevent it from being stolen by others.

After protection, the three yards can be directly glued with opaque tape.