Powershell Set-MpPreference -DisableRealtimeMonitoring $true not working correctly

The problem is that the Windows Defender antivirus services seem to be persistently disabled on your machine.

It's unfortunate that the Set-MpPreference cmdlet reports this in such an obscure fashion.

To fix this problem, re-enable the Windows Defender antivirus services:

The easiest way to do this is the following, but note that it involves a reboot:

Set-ItemProperty 'HKLM:\SOFTWARE\Policies\Microsoft\Windows Defender' DisableAntiSpyware 0Restart-Computer

• You may instead use the Local Group Policy Editor-based method described in this windowscentral.com article or use regedit.exe's GUI or us the reg.exe CLI utility.

  • Note that the linked instructions are slightly outdated - instead of node Windows Defender, setting Turn off Windows Defender, target node Windows Defender Antivirus, setting Turn off Windows Defender Antivirus).

  • While using the Local Group Policy Editor (gpedit.msc) to turn the antivirus services off takes effect immediately, turning them back on can take minutes before the services are actually restarted (on the plus side, no reboot is required, unlike what the linked instructions say).

• Note that if you reenable via the registry, such as via the above PowerShell command whereas disabling was originally performed via [local] group policy, that policy will continue to reflect the disabling (however, it is the registry setting that matters).