In order for Sara, a client, to logon to her desktop computer, she must provide her username, password, and a four digit PIN. Which of the following authentication methods is Sara using?

Three-factor authentication would require one credential each from three different categories: something you know, something you have, and something you are.

Despite providing three pieces of information, Sara is using single-factor authentication because username, password, and PIN are all 'something you know' credentials. Multi-factor authentication requires credentials from at least two distinct factor categories (know, have, are/biometric). Using multiple credentials of the same type does not constitute additional factors.

Two-factor authentication requires credentials from two distinct categories, such as a password combined with a smart card or biometric.

Four-factor is not a recognized standard authentication classification; it does not correspond to any defined factor category model.