A SIEM is not a security team in a box. It is a search and correlation layer over telemetry. The quality of its output depends on the data you feed it, the rules you write and the analyst who interprets the result.
What a SIEM actually does
- Ingests logs from endpoints, identity, network and cloud.
- Parses them into a common schema so fields are searchable.
- Correlates events across sources, often with time windows.
- Alerts when a rule or analytic matches.
- Stores the data for investigation and retention.
The hard parts are parsing and context. A rule that fires on powershell.exe is noisy. A rule that fires on an encoded PowerShell command spawned by an Office process is far more useful.
Alert quality beats alert quantity
A queue with 500 alerts a day trains analysts to close without reading. That is a security failure disguised as productivity.
Good detections have:
- a clear behaviour they describe;
- known false-positive drivers;
- a documented response;
- an owner;
- a test that proves they still fire.
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