3-digit card verification number

As an added security, almost all credit cards today have a 3 Digit Card Verification Number.
For your safety and security, PayPal requires that you enter your card's verification number. The verification number is a 3-digit number printed on the back of your card. It appears after and to the right of your card number.

See examples -->

For Visa, Mastercard and Discover, it is a 3-digit number, see below:

For American Express cards, the card verification number is four digits, see below: