3-D Secure is an XML-based protocol used as an added layer of security for online credit and debit card transactions. It was developed by Visa to improve the security of internet payments and offered to customers as the Verified by Visa service. Services based on the protocol have also been adopted by MasterCard, under the name MasterCard Secure Code. 3-D Secure adds another authentication step for online payments. 3-D Secure should not be confused with the Card Security Code (commonly known as CVV) which is a short numeric code that is printed at the back of the credit card.