It could be Malware, but it's probably just Microsoft..
Uninstall Defender, and they suggest reinstalling which should work.. (Though there r others out there, which r better)
That was ( a couple of years ago) a common error with defender, not now though, those bugs should be out of it.
The last couple of times I've seen it, it's being a symptom of a machine with a Fake AV program on it..