What should be your primary focus after identifying a compromised user in Office 365?

The primary focus after identifying a compromised user in Office 365 should be on initiating a password reset and enforcing multi-factor authentication (MFA). This is crucial because resetting the password directly addresses the immediate threat posed by unauthorized access. It ensures that the compromised account cannot be accessed again using the previously obtained credentials.

Additionally, enforcing MFA significantly strengthens account security by requiring a second form of verification, which drastically reduces the risk of further unauthorized access, even if an attacker has somehow retained knowledge of the user’s password. These steps are fundamental in incident response and help contain the breach, safeguarding sensitive data and other accounts before further investigative measures are taken.

While reviewing email clusters for malicious content, blocking URLs, or conducting a user pivot all serve important roles in threat investigation and remediation, the immediate priority must be to secure any compromised accounts to prevent further damage. Addressing the compromised status of the user account is vital before moving on to other investigative actions that may help in understanding the context and extent of the breach.