How does "Two-factor Authentication" enhance security in Exchange Online?

Two-factor Authentication (2FA) significantly enhances security by adding an extra layer of protection beyond the traditional username and password. In Exchange Online, when 2FA is enabled, users are required to not only enter their password but also to confirm their identity through a second verification method. This could include receiving a code via text, using an authentication app, or confirming a login attempt through a biometric method such as a fingerprint.

This approach drastically reduces the risk of unauthorized access. If a user's password is compromised, an attacker would still need the second form of authentication to gain access to the account, thereby adding a critical barrier against potential breaches.

Other options, while addressing security aspects, do not encapsulate the core function of two-factor authentication. Limiting access to administrators or creating complex passwords can improve security but do not provide the dual-layer of protection that 2FA offers. Similarly, limiting login attempts is a different security measure aimed at preventing brute-force attacks rather than verifying user identity during the authentication process. Overall, the requirement of an additional verification method is what truly characterizes the strength of two-factor authentication.