Two-factor authentication

Two-factor authentication is a form of identification often used in making sure a credit card transaction is authorized. Typically one factor may be a physical object (such as having a credit card in your possession), another may be a piece of knowlege (such as a PIN number or security code number), and yet another may be a unique characteristic (such as a fingerprint, an iris pattern or the ability to retype a sequence of numbers and letters). The presence of two factors allows a two-factor authentication.