An authentication system that requires a username, password, and PIN is known as what?

The correct answer is that an authentication system requiring a username, password, and PIN is categorized as multi-factor authentication. Multi-factor authentication (MFA) involves using two or more different factors for verification. These factors often fall into three categories: something you know (like a password), something you have (like a token or a smartphone for receiving a PIN), and something you are (like a fingerprint or other biometric data).

In this case, the username and password act as one factor (something you know), while the PIN adds another layer of security (potentially something you have or know). By requiring both a password and a PIN, the system significantly increases security by ensuring that even if one factor is compromised, unauthorized access is more challenging.

On the other hand, options referring to single-factor or two-factor authentication do not accurately describe the situation here. Single-factor authentication would only involve one method of verification, while two-factor authentication requires two distinct verification methods but may not include three factors like in this case. Multi-layer authentication is a term that isn’t standard or well-defined in terms of security measures. Hence, multi-factor authentication is the most appropriate definition for a system using a combination of username, password, and PIN for authentication.