Is it safe to add exclusions?

For trusted folders (your own source code, a Steam library, a VM image you trust): yes. Don't exclude downloads or temp folders.

△ Performance

Windows Defender high CPU (Antimalware Service Executable)

MsMpEng.exe (Antimalware Service Executable) is Windows Defender. High CPU from it is almost always its self-scan task — Windows Defender Scheduled Scan — or real-time protection looping on a folder it shouldn't be scanning.

Time: 10 min
Difficulty: easy
Applies to: Windows 11, Windows 10
Updated: May 25, 2026

Symptoms

▸Antimalware Service Executable using 30%+ CPU continuously
▸Spikes happen at specific times of day (scheduled scan)
▸PC fan ramps up during file copies or large-file operations

Likely causes

▸Scheduled Defender scan currently running
▸Real-time scan looping on a folder full of small files (node_modules, source control)
▸Conflict with a second antivirus product

How to fix it — step by step

01
Check the Defender scheduled task
Task Scheduler → Microsoft → Windows → Windows Defender → Windows Defender Scheduled Scan → Properties → Conditions. Untick Start the task only if the computer is idle and set a specific time.
02
Add exclusions for hot folders
Windows Security → Virus & threat protection → Manage settings → Exclusions. Add your code repos, large Steam library, VM folders.
03
Cap CPU usage
Limit Defender to a percentage of CPU:
```
Set-MpPreference -ScanAvgCPULoadFactor 30
```
04
Remove any third-party antivirus
Two real-time scanners on the same machine fight for every file read. Pick one.