Sigma rules are human-readable detection rules for security logs. They describe suspicious behaviors in a common format, such as failed logins, unusual process launches, or known attacker patterns, and can be translated into queries for different SIEMs and other detection tools.
They matter because they help teams write detections once and reuse them across platforms, which reduces lock-in and speeds up sharing. In real defenses, analysts use Sigma content to detect malicious activity in endpoint, network, or identity logs. In attacks, adversaries may try to evade these rules by changing commands, using legitimate tools, or blending into normal activity. Good Sigma rules depend on clean parsing, normalized fields, and careful tuning to avoid false positives and missed alerts.