The three-digit code on the back of your Visa® card is one more layer of security. Also known as the Cardholder Verification Value or CVV2 (or more commonly, CV Code), these three numbers help ensure that the physical card is in the cardholder's possession while shopping online or by phone. This helps to prevent unauthorized or fraudulent use by someone who may have obtained your card number and expiration date, but doesn't have the physical card.
Where can I find it?
The 3-digit code is located on the back of your card, inside the signature area. Typically the signature panel will have a series of numbers, but only the last three digits make up the CV Code.
What does it do?
It's actually more about what it prevents. When shopping online or over the phone, the 3-digit code helps merchants ensure that the card is in the right hands. Merchants will request the CV Code at checkout from the cardholder, and the information is sent electronically to the card-issuing financial institution to verify its validity. Within seconds, the CV Code results are returned with authorization. If it's returned invalid, merchants have the right to stop the transaction.
And for your added protection, merchants are prohibited from keeping or storing the CV Code number after the transaction has been completed.