Concurrent account lockouts following a series of failed login attempts are indicative of a password attack, potentially a password spraying attempt where an attacker uses a common password against many accounts before moving on to try a different password, to avoid account lockout thresholds. Account lockouts are a common indicator of such attacks. The other options are potential indications of malicious activity, but they are not as closely related to the scenario of multiple user accounts being locked out due to failed login attempts.