I am going to sound pompous here, but I'm really unsure of how people get a virus with Defender+an AdBlocker. Are you going to shady sites? Are you downloading shady material? I'm pretty confused.

Mainly "drive by" downloads. So adblocker isn't 100%, close, but not 100%. And some sites get infected, especially smaller blogs and such. You go to that website, it tries to download bad shit to your computer.

Many are flash downloads, so once flash DIES that'll help us all.

I manage the AV for thousands of PCs, and our users CANNOT run as administrator - and about 95% of our users are doing so through our Proxy, which filters out virus and malware before they even get to a PC. Yes, we have viruses hit our systems. If you feel that running defender + adblock leaves you 100% protected - you're being a bit over confident.

Now if you run defender + adblock - AND also run as a user (NOT an Admin), your security stance will be super solid. Assuming you ARE updating your OS and software packages. If you aren't updating software, even little stuff like Foxit PDF reader - you're leaving yourself extraordinarily vulnerable.