The CVC (Card Verification Code) of the Great Wall VISA card is a three-digit security code, which is usually located behind the signature column on the back of the card. On most VISA cards, the CVC code is next to the last three digits of the card number. You can flip through the card and find the three digits behind the signature column. This is your CVC code. If you can't find the CVC code or have other problems, I suggest you contact the customer service of Bank of China for help.