The holder inquires the security code himself and looks at it in kind. That is, there are seven (or eight) bold characters on the back of the credit card, the first four digits are the mantissa of the bank card number, and the three or four digits behind the space are the security code.

The generation method of 1. is that the bank extracts the card account number, validity period and service code, arranges them and then calculates them through a series of complicated algorithms. After this set of numbers is generated, only the issuing bank and the holder of the bank card know what this number is.

2. This is the security code of the credit card when conducting online or telephone transactions. It is usually used to prove that the payer has a credit card at the time of transaction, thus preventing credit card fraud.

3. The credit card used for a long time is not properly kept, which leads to ambiguous numbers. You can cover it with a thin piece of white paper and slowly smear it in the corresponding position, which is generally visible. Write down the security code in a private book or write it by hand. When you forget the security code or the security code is not clearly displayed, take it out and check it. If you really can't view it, you can also apply for a new card from the bank, that is, cancel the original card and replace it with a new one. The security code after card replacement is the same as that of the previous card.

The security code of 1.VISA card is called CVV2, which has three digits and is printed on the last four digits of the card number on the back of the credit card.

2. The security code of MasterCard is called CVC2, which has three digits and is printed on the last four digits of the card number on the back of the credit card.

3. The security code of the 3.discovery card is called Cardmember ID, which has three numbers and is printed on the signature column on the back of the credit card.

4. The security code of American Express Card is called CID, which has four digits and is printed on the front of the credit card above the credit card number.

5. The security code of UnionPay card is called CVN2, which has three digits and is printed on the back of the credit card after the last four digits of the card number.

6. The security code of 6.JCB card is called CAV2 (card authentication value 2), which has 3 digits and is printed on the back of the credit card number.