My computer got infected by a virus (one that Windows Defender did not detect) last week. I ran a Norton Bootable Rescue CD I had made and that cleared out the virus for good. However, when I went to the Windows Defender Windows, it told me that I already had an antivirus running and thus was switched off. Believe me, I have no anti-virus running.
I realized that this was one of the after effects of the virus (or maybe it was still running) and thus I resetted my PC. After that I had no problems.
Now, I'm just curious, How exactly does Windows Defender know that an antivirus is running?
I have Windows 10 Version 1607 (AKA, The Anniversary Update).
Best Answer
Windows Defender will only know if you have an antivirus program running if that antivirus program reports itself to your windows system. Here is a link that says this from Microsoft themselves: Link