Look at the front of your card. Your Security Number is the four-digit number above and to the right of the embossed card number.
VISA, MasterCard, Discover:
Look at the back of your card. Your Security Number is the three-digit number at the top-right corner of the signature strip.
Why do you need my Credit Card Security Number?
By asking you to verify your security number, we are taking an extra precaution to protect you against fraud. Credit card companies incorporate these numbers for situations where merchants cannot visually verify that you have the credit card in YOUR possession, such as Internet transactions.