The security code of a credit card is the security code that the cardholder needs to input when conducting off-site transactions such as internet and telephone or transactions without a card. Cardholders should properly keep the security code of their credit cards. If they accidentally reveal it, there may be a risk of theft. There is no way to check the security code except looking at the back of the credit card, even if you call the customer service hotline of the issuing bank. For users, just remember the 3-digit security code, and at the same time pay attention to keeping the credit card well, and don't disclose the relevant information of the security code.