no.

no virus would even try to do that it doesn't make sense.


it's most likely a corrupt download cache for defender

Defender can be updated through Windows Update. Usually works a lot better. I would give that a try.

actually many virus prevent updates and simulate programs functioning.
in this case I don't thing its related though as there should be other issues along with it.

Viruses can fuck up your internet connection though, and in general could result in updates not happening

Manually downloading the update should work just fine. Google something along the lines of "most recent windows defender update" and then look for a link from Microsoft in the results, or try Windows Update. Good luck