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If Windows Security crashes when you open Protection History, first check whether Defender reports a threat that still needs action. Do not treat deleting Detections.log or clearing history as malware removal: Protection History records events, while threat remediation is a separate step. A locked log file is not, by itself, proof of malware or corruption.
Check for an active threat before troubleshooting the crash
Protection History is a record of Defender actions, potentially unwanted apps that were removed, and important security services that are turned off. An old entry does not establish that a threat is still on the PC. When the page opens, review the event and its status; Microsoft says threat details require administrator privileges. If an item says action is needed, use the event’s Actions menu. If you are unsure whether a detected item is safe, Microsoft recommends quarantine rather than allowing it. Microsoft’s Protection History guidance
Clearing an event record is not a substitute for handling an active detection. If the interface crashes before you can inspect an event, do not assume the history is harmless or that deleting its files will remediate anything; establish current threat status through Windows Security or appropriate Microsoft support.
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Record the crash details before changing Defender files
The available reports do not establish one cause or a universal repair for this crash. Capture details that can help distinguish a page failure from an active detection or file-lock problem:
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- Your Windows edition, version, and OS build.
- Microsoft Defender platform and security intelligence versions.
- What happens when you select Protection History: whether the app closes, freezes, or shows an error, and the wording or code if one appears.
- Any coincident error in Windows Event Viewer’s Application log.
- Whether Windows Security shows a current detection or remediation requiring action.
Why detections.log may not delete
Detections.log is in a Defender-protected area and may be in use by a running service or blocked by Windows permissions. A Microsoft Q&A user reported that Detections.log and a related binary remained in use during a broad cleanup attempt; that report does not show that the log should be force-deleted or that it caused the Protection History crash. Microsoft Q&A discussion of the locked file
Do not disable Defender, take ownership of protected files, or force-delete the individual log as a routine fix. The cited material does not provide official Microsoft instructions to remove Detections.log alone.
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Choose a response based on what you need to fix
| Option | What it does | Evidence and cautions |
|---|---|---|
| Handle an event that needs action | Addresses the detection through its Actions menu; quarantine is the cautious choice when unsure. | Microsoft-documented guidance. It targets the threat, not the crash itself. Microsoft Support |
| Adjust scan-history retention | Sets how long scan-history items are kept; it does not clear history immediately or repair the crashing page. | Microsoft-documented PowerShell preference. Microsoft Learn |
| Remove history folders | May erase stored history records, not remediate an active threat. | Community-reported workaround for similar crashes, with variable outcomes; it is not an official Microsoft repair. Microsoft Q&A discussion Another community report |
Set age-based history retention with PowerShell
If your aim is ordinary retention management rather than fixing a crash, Microsoft documents Set-MpPreference -ScanPurgeItemsAfterDelay to control how many days scan-history items are kept. The documented default, when no value is specified, is 15 days. Microsoft also shows 30 days as an example configuration for Defender for Endpoint; that is an example, not the default. Set-MpPreference reference Defender for Endpoint remediation guidance
Run PowerShell as an administrator and use the setting only if you intend to change retention:
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Set-MpPreference -ScanPurgeItemsAfterDelay 30This example configures 30 days; choose a value appropriate to your retention needs. Microsoft does not claim that changing this setting repairs a Protection History crash. It is a retention control, not an immediate deletion command or malware-removal step.
When to consider the community-reported folder workaround
Several Microsoft Q&A replies suggest deleting files under C:ProgramDataMicrosoftWindows DefenderScansHistoryService or its DetectionHistory subfolder for similar crashes. Some replies mention Safe Mode. These are community suggestions, not Microsoft-documented repair steps, and reports include failures or recurrence. Community suggestions for a similar crash Additional community reports
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Folder deletion can remove history records and its result may vary. Do not apply a broad deletion to the Defender Scans tree or use it to address an active detection. If the crash is reproducible and you are considering this workaround, preserve needed information first and seek guidance suited to your Windows build rather than improvising around protected files.
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What Protection History retention means
Microsoft Support says Protection History retains events for two weeks before they disappear from the list. The Defender PowerShell reference separately documents a 15-day default for scan-history items when ScanPurgeItemsAfterDelay is unspecified. These figures describe different documentation contexts; the 30-day value above is an example setting, not a general default. Protection History retention Scan-history retention preference
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