A credit card's issue number differs depending on the particular brand. It is used when the card holder is not physically present, such as buying goods online, and therefore is intended to protect the card holder against misuse and fraud. For MasterCard credit and debit cards, the issue number is also called the CVC2 code.
The MasterCard issue number is found on the reverse side of the card, in the signature box. It is the last three digits of a longer numerical code.
The issue number is used when the customer is not physically in a store, but instead buys items virtually. It may also be used when the magnetic strip fails to work properly. It is therefore a security feature for the purposes of fraud prevention.
It should be noted that the issue number on a MasterCard credit or debit card does not safeguard against phishing scams. A customer may be tricked into giving his or her issue number to someone else in such scams. Caution should be exercised, as no credit card is completely fraud-safe.