3D Secure, marketed as MasterCard SecureCode and Verified by Visa, is a technique for helping protect your payment information when you shop online and pay with a credit card.  You set up a password for your credit card with MasterCard or Visa at the links below, and at online checkouts you have to enter the password for the charge to be approved.  That gives you an extra level of protection if someone steals your credit card number.  

Not all credit card companies offer MasterCard SecureCode or Verified by Visa.  In addition, online stores have to make changes to their Web sites to check for these online passwords.  Thousands of online stores do work with MasterCard SecureCode or Verified by Visa, but many do not.  

For more information, visit the Visa  and Mastercard websites