Only for your 1st paragraph, I too experienced that encounter but there’s an explanation for this from the Microsoft Community that I researched about this

https://answers.microsoft.com/en-us/protect/forum/protect_other-protect_scanning/two-infected-files-shown-during-oct-2016-malicious/fb273053-6bd7-45ba-9710-8b5e5ff0469c?lc=1033