Security Intelligence is the threat-definition layer used by Microsoft Defender Antivirus. It is the continually updated intelligence that helps the engine recognize malware, suspicious behavior, and known attack patterns. In practice, these updates can include signatures, heuristics, and detection rules that tell Defender what to block or quarantine. Because the layer changes frequently, it is a critical part of endpoint protection: if it is stale, Defender may miss new threats; if it is broken, scans and detections can fail or behave unpredictably.
In real-world defense, Security Intelligence is delivered through the update path, so teams monitor its version, deployment status, and update health. Attackers benefit when definitions are outdated, because freshly modified malware may evade detection longer. Defenders respond by testing updates before broad rollout, keeping rollback procedures ready, and correlating antivirus results with EDR telemetry and logs. In short, Security Intelligence is the moving knowledge base that keeps Defender current and useful.