There is a 7-digit number on the back of a credit card, which is usually used to verify that the payer owns the credit card at the time of transaction, thereby preventing credit card fraud. The first four digits are the last four digits of the credit card number, and the last three digits are the credit card security code, which is a security code for the credit card when making online or telephone transactions.

The credit card security code is generated by the bank extracting the card account number, validity period, and service code, arranging them, and then calculating them through a series of complex algorithms. After this set of numbers is generated, only the issuing bank and the bank card holder know what the number is. Whether it is a VISA or MASTER credit card, the principle of generating a security code is the same. The main function of the credit card security code is as a verification code for online transactions or credit card account cancellation.

The three-digit number on the back of the credit card is equally important as the cardholder's signature. It is considered a "confidential" of the credit card and should be kept properly by the cardholder. It is recommended that credit card holders who frequently conduct online transactions must ensure the safety and legality of the merchants with whom they conduct transactions, and prevent the digital information on the card from being leaked to unrelated persons, otherwise it will pose a security risk to their credit cards. The last three digits also play a very important role in preventing the card from being cloned. Because if criminals obtain the credit card account information and copy the card, but do not copy the "last three digits" information, even if they know the password, the ATM will refuse the withdrawal.

Instructions for security code protection

1. After getting a new card, it is recommended to use a small sticker to stick the security code on it to prevent leakage.

2. In recent years, anyone who receives any information (phone, text message, WeChat, QQ, email, etc.) asking for a security code by obtaining a security code is a scammer. Do not be fooled.