I used to use Malwarebytes, but recently they got an update and they seem more invasive with constant pop-ups to buy their premium package, etc. I uninstalled it a couple weeks ago and now I have a virus (just some low-tier phishing scam when I open microsoft.com in browser). So I think it installed a backdoor.

What is the good trustworthy antivirus now? Preferably GNU free-as-in-freedom but I know that's a lot to ask. Let's say free-as-in-cost at a minimum.