Prevent windows defender from scanning during games

I was surprised as well, since googling the problem mostly returned the answer that "it should only run when your system is idle". Nevertheless, this is just a screenshot from yesterday.

I will try Jsssss suggestion as you advice as well!

I get exactly the same problem as Zsigma:

• Windows 10 Pro x64
• WIndows Defender process MsMpEng.exe will unpredictably take up to 50% of CPU.
• If this happens whilst I am playing games, then the game will lag badly.
• Windows Defender is not running a schedule scan.
• Procmon shows Defender is accessing lots of my documents etc files.
• Turning off real-time protection whilst gaming is a workaround, but it is not ideal.
• What I really what is for Defender to detect that my PC is not idle and therefore to stop hogging the CPU.

You could use either Option 5 or Option 6 in this guide:

Turn On or Off Windows Defender Real-time Protection in Windows 10

Those options will let you disable Windows Defender Real-time Protection without being prompted it is turned off, and without it getting automatically turned back on later by Windows.

Meaning you can disable Windows Defender Real-time Protection as long as you wish, and then easily re-enable it when you're finished with your games.

So I leave this unsolved. While I can disable and enable windows defender using the guide Jssssss linked, this is not really a solution, as it is a workaround. I will go to a 3rd party antivirus again, solely because of this issue. I hope microsoft fixes this

The Antimalware Engine runs from startup to shutdown providing real-time (on-access) protection. It consumes CPU as it continuously scans all files involved in file system read/write operations, with the CPU utilization of the Antimalware Engine being proportional to the level of file system read/write activity.

Automatic Maintenance triggers the Windows Defender Scheduled Scan task on a “daily” baseline frequency, but this task normally fails to start. When it does start, it runs with an only-on-system-idle priority. Because this scan is terminated by any user activity, it’s very difficult to monitor, and the simplest way to make sure that it’s not running is to disable the Windows Defender Scheduled Scan task in Task Scheduler.

You should try just turning off real-time protection in the Windows Defender Security Center app before you resort to a “permanent” solution. If you feel compelled to use Group Policy in order to turn off Defender’s real-time protection (and turn it back on again later), then you can do that very quickly with these commands:

Right-click on the Start button and select Windows Powershell (Admin) and then copy, paste, and enter the command:

Turn off Windows Defender’s real-time protection:

REG ADD "HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection" /v DisableRealtimeMonitoring /t REG_DWORD /d 1 /f

Turn on Windows Defender’s real-time protection:

REG DELETE "HKLM\SOFTWARE\Policies\Microsoft\Windows Defender\Real-Time Protection" /v DisableRealtimeMonitoring

But the only indication that you’ve just turned off all Antivirus/Antimalware protection will be this: 

This setting is managed by your administrator:

In case it isn't clear, you can't just leave real-time protection turned off; and you really shouldn't disable Defender's real-time protection unless you're offline. So, depending on the circumstances, you might be better off looking for a free AV solution that comes with a built-in gaming mode.

GreginMich