Defender Event ID 2001: Security intelligence update failed
The security intelligence update failedDefender event 2001 is logged when a security intelligence (signature) update fails, with the versions, update source and error.
2001
- Event ID
- 2001
- Channel
- Microsoft-Windows-Windows Defender/Operational
- Provider
- Microsoft-Windows-Windows Defender
- Log file
- Microsoft-Windows-Windows Defender%4Operational.evtx
- Category
- Antimalware
- Default logging
- Logged by default
What event 2001 means
Event 2001 records a failed update of Defender's security intelligence (definitions). It includes the current and attempted versions, the update source (Microsoft Update, WSUS, file share…) and the error.
Occasional failures are normal on laptops and isolated networks. A long run of failures leaves the host with stale definitions, and blocked updates are one of the quieter ways an intruder can weaken protection.
When it is logged
Audit policy / configuration
None — logged by Microsoft Defender Antivirus when it is the active antivirus.
Key fields
| Field | What it tells you |
|---|---|
| Current Signature Version | Definitions version installed before the attempt. |
| Update Source | Where the update was requested from. |
| Error Code | Error returned. |
| Error Description | Text of that error. |
Common benign sources
- Offline machines, proxy problems, WSUS misconfiguration.
What attackers do that produces it
- Update sources blocked or tampered with (hosts file, firewall rules, proxy settings) to keep definitions stale.
Investigation tips
- Check how long updates have been failing and whether other hosts on the same network are affected.
- Look for firewall rule or hosts file changes near the start of the failures.
Sigma rules for this event
No bundled SigmaHQ rule targets this event ID specifically. Rules on related events may still cover the activity.
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