The rule 'Duo User Action Reported as Fraudulent' is designed to detect and alert when a user reports a Duo authentication action as fraudulent. This can often indicate potential malicious activities or account compromises. The rule triggers an alert whenever the log entry indicates that a user has marked their authentication as fraudulent. With a medium severity level, it captures instances of user behavior where a legitimate action is flagged indicating possible security incidents. The detection relies on logs from Duo's Authentication services which provide detailed records of user activities and status, and this specific rule looks for a specific reason 'user_marked_fraud'. The deduplication period set to 15 minutes helps to reduce alert fatigue by consolidating multiple similar alerts into a single notification during this window. In practice, the runbook suggests following up directly with the user for immediate verification of the claim to mitigate any possible security threat quickly.