Antivirus recommendations

[User0001]

Windows Defender or Malwarebytes.

[Ivybridge11]

I generally use Windows Defender with Malwarebytes free as the second line, which I run about once a week to check for anything that got past Defender.

[AnyOldName3]

Even if you don't regularly run Malwarebytes, it's good to keep it installed in case you use your computer while drunk/sleepy and give admin access to something you shouldn't have. It's pretty good at clearing out malware once it's already on a system even if you don't pay to get real-time protection.

If you're not doing anything stupid, the built-in Microsoft stuff is pretty good these days. It used to be that once every couple of years, they'd decide to support it and release a set of updates which made it one of the best and then forget about it and let it become outdated, but they've been pretty consistent about keeping it updated recently.

Before that, I used Avast, but I got loads of false positives and had to keep it in gaming mode to hide the ads, which then means that you don't get a notification when it blocks something (which was a massive pain when it decided that everything I built with Visual Studio 15 was malware for a few months). The last straw was when I cocked up and approved a program's request for admin access on autopilot, even though I didn't trust it. Despite real-time protection being on, Avast made no attempt to save me from my mistake, even though it was supposed to.