The CVV / CVC is used to help validate that a customer has physical possession of the credit card being used.
With a Visa, Master Card, or Discover Card the security code is the last group of numbers printed on the back side of the card and is 3-digits.
With an American Express Card the code is 4-digits long. It can be found on the front side, above the credit card number on either the left or right of the card.
