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After 3 years of using my laptop, I decided it’s time to format and reinstall Windows 10 from scratch. Everything went smooth, no issues. However I noticed in the task manager that the process “Antimalware Service Executable - Windows Defender Antivirus Service”, is constantly at 20% CPU usage. Looking at the resource monitor, the file is called MsMpEng.exe

First I thought it’s just an initial scan after the new installation of Windows. But now it’s been 5 days later, been working on the laptop each day for about 12-16 hours, restarted multiple times per day, and no matter what, it’s always at 20% CPU usage. Even when I go to bed and leave the laptop on, 7 hours later, it’s still at 20%.

After a restart it takes about 5-10 minutes until the process Windows Defender Service starts to be at 20%.

It’s a fresh installed legal and activated version of Windows 10 home.

Very little software has been installed so far, and I have very little files in my document folders. No external hard drives or USB sticks attached.

Checking the antivirus options, it does not show that it’s scanning, so I don’t know why it’s constantly at 20%.

Deactivating Real-time Windows Defender protection also makes no difference. If I disable it, it’s still at 20% CPU usage.

Also I can’t end nor stop the task in Task Manager, it tells me Access Denied, even as admin.

As I said, this is not just a short period that it’s at 20%. It’s constantly at 20% for the past 5 days. This has not been the case before I formatted my laptop.

Update:

After monitoring task manager and the resource monitor, I also noticed the Disk Usage jumps every few seconds to 30MB/s - 80MB/s from the process Defender Antivirus Service (MsMpEng.exe) and "service".

Even though I just restarted and have no apps open (apart from the regular background apps), "service" is constantly writing to "C:\Windows\Temp" creating files that are several 100MB big. The disk activity created by "service" is constantly at 100KB/s - 500KB/s, reading and writing to the Temp folder.

MsMpEng.exe has two processes running and is constantly reading and writing to C:\ProgramData\Microsoft\Windows Defender\Scans\mpenginedb.db-wal and C:\$LogFile (NTFS Volume Log) with 10-50KB/s.

This seems strange behavior because it also occurs when I restart the laptop and don't open a single program.

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On my machine, Defender was constantly scanning Veeam Logfiles. Adding c:\ProgramData\Veeam - Folder to the exclusion list calmed it down immediately.

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Adding the folder "C:\ProgramData\Microsoft\Windows Defender\" to the exclusion list of Windows Defender seems to have done the job.

Open up Window Defender Security Center -> Virus & Thread Protection -> Virus & Thread Protection Settings -> Exclusions -> Add or remove exclusion -> Add Folder -> ""C:\ProgramData\Microsoft\Windows Defender\"

Restart PC.

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