If you are doing a banking transaction online, there is very little chance that you would not have to key in the Card Verification Value or the CVV.
This is one line of measure that helps you to protect your card against any fraud when transacting online.
You should just look behind your card and you would be able to see a three digit number, which is the CVV. It's important that you do not disclose this number to anybody.
How do you know this CVV?
Just reverse the card and you find a magnetic tape. On this there is a large amount of data that is normally stored. In fact, this tape is very important as it picks-up all data.
Beyond that you can celarly see a multi-digital numbers, which are three numbers, which is in fact the Card Verification Value.
Different cards provide different numbers. For example, MasterCard and VisaCard has 3 numbers, while in the case of American Express Card it is 4 numbers.
One has to wait and see the newly introducted Rupay Card in India has how many numbers. Below this is the panel where you sign on the card.
What is the importance of the CVV?
It is just an additional line of security, that provides some protection, when you transact online. For example, if the magnetic tape where the CVV is tampered, there would be an instant reading that it is a damaged card.
However, you cannot be protected against frauds all the time, just because of this 3 digiut number. Tthere is no way that this will help you, if you have been tricked into giving out information with regards to the CVV.
On the other hand there is no protection also against a stolen and lost card, where this number reaches nefarious hands.
It is very important that you do not divulge details on the Card Verification Value. This is because, you will be otherwise vulnerable to frauds. Prevention afterall is better than cure.