I will consider this. I "maintain" my relatives computers which is basically to install an anti-virus and adblock. They still get those sketchy messages from friends from time to time though, which is the main reason that I keep them with an AV. Is this correct? Does AV improve security for people who cannot differentiate between a .pdf and an .exe?
Personally I don't use an AV, I am a bit paranoid and technical competent so my case and my relatives is totally different.
I don't use an AV either, but I'm very careful with the things I download (and I don't download new stuff very often).
My relatives, on the other hand, will click just about anything that says "click me" (even more if it says they will win a prize or something).
Windows Defender is great and it's enough for me but my relatives need something that cover more areas. Any way you can think of tricking them, they will fall for it. Even with AV, they routinely install malware (those that are too new to be in the AV database or using new techniques not covered by heuristics).
As far as I know, my relatives don't do anything but sit in front of their computers trying to install malware ;)
My love for Windows Defender came when it was called Giant Anti-Spyware (founded by Oz). It managed to find 4 pieces of spyware on my computer, and I consider myself technically competent enough to clean spyware manually.
When I ran the same software on another computer, it managed to find 3284 pieces of malware. And to think I was planning on doing it manually, eh eh. (It had an antispyware software that did nothing.)
Eventually, Giant went mainstream and malware became smarter to work around it. At which point, MBAM came to the rescue. My next favorite anti-malware.
Personally I don't use an AV, I am a bit paranoid and technical competent so my case and my relatives is totally different.