After a manual deinstallation of Trend Micro Worry Free Business Security 9.0,
Windows Defender did not automatically see that it could turn on its antivirus component.
It took me a while to find this solution, so here is a repost.
- Press Win key + R. This will open Run.
- Type “regedit” and hit enter.
- Navigate to these keys:
- Change value of ‘DisableAntiSpyware’ and ‘DisableAntiVirus’ from ‘0’ to ‘1’.
- After changing the values go to ‘C:\Program Files\Windows Defender’ and open ‘MSASCui.exe’ file.
If the gui is already open, close it first and then relaunch using MSASCui.exe.
Hope this helps you!