I subscribe to the forum windows10 on reddit ( https://www.reddit.com/r/Windows10/
) and on there Microsoft's Windows Defender is the antivirus software of choice. Microsoft is regularly updating its antivirus definitions, every day if necessary. I've never used anything but Microsoft's antivirus software because I keep hearing about (or helping) people having problems with 3rd party antivirus software screwing things up. On that forum they are also unanimous about being sure to let Windows apply updates from Microsoft as they become available (they often include security updates), which of course I always do as well.