The O365 Excessive Single Sign-On Logon Errors rule is designed to detect potentially malicious activities associated with accounts that experience a high volume of SSO logon errors in Microsoft 365. This is often indicative of a brute force attack on user accounts, using incorrect credentials or expired tokens. The rule leverages data from Office 365 audit logs, specifically monitoring for the 'SsoArtifactInvalidOrExpired' error associated with authentication attempts. The detection logic triggers an alert when five or more errors occur within a 20-minute window per user. Analysts are advised to investigate unusual patterns, analyze timestamps, and correlate findings with related security events to confirm if the errors are due to legitimate user actions or malicious activity. Proper response includes isolating affected accounts, enforcing strong password policies, and implementing multi-factor authentication to safeguard against attacks. False positives may arise from legitimate user behavior, automated systems, or misconfigured MFA scenarios, thus requiring careful analysis before escalation. The risk score of 73 categorizes this alert as high severity, emphasizing the importance of timely investigation and mitigation. The rule is integrated with various Microsoft 365 services and is part of ongoing incident response and security monitoring strategies.