The card security code is a unique three or four digit number, separate from your credit card number. Your security code can be found in the following locations on the following cards:

Visa/MasterCard
Your card security code for your MasterCard or Visa card is a three-digit number on the back of your credit card, immediately following your main card number.

American Express
The card security code for your American Express card is a four-digit number located on the front of your credit card, to the right of your main credit card number.