3-D Secure, also known as “Payer Authentication”, is a security protocol that adds an extra layer of protection to your online debit/credit card transactions. Different card networks have developed their 3-D Secure systems, so your authentication will be branded with messages like “Verified by Visa” or “MasterCard Secure Code”. Whenever you receive an authentication request, simply enter the one-time PIN you receive via SMS into the required field.