If the three digits on the back of a credit card are known to others, it is likely that the credit card will be stolen and the cardholder's information will be stolen by illegal parties. The three-digit number on the back of the credit card is the credit card security code, which can support "offline payment", even if you don't have an actual card, you can make purchases. It is recommended to cover it with opaque tape at ordinary times, which can prevent people from seeing it and does not hinder daily use.