I have been trying to help my grandpa sort out some issues with his computer (cleaning up useless programs, registry, defrag, all that fun stuff) and I was wondering what the best antivirus program for him to use is. He had about three bogging down the whole system and I'm trying to pick one for him. Personally I use MSE, but for him I think something that does as much as possible with minimal user involvement would be best, and it helps if it's free too. I'm thinking of going with Avast right now, but I'd appreciate any advice. Thanks!

Certainly Avast.Its pretty much instal and go.it updates its definitions and updates the program itself.In fact,I installed it on my great aunts PC about a year ago,so far so good.

I'm using Avast free version and its great. There's a commercial version but the free version is good enough for the average home user. I've been using Avast for 4 years and I haven't had any complains really.

Not really an anti-virus, but having Malwarebytes is decent to have for removing stuff an anti-virus doesn't remove.

I also suggest looking into CCleaner for cleaning up extra data, programs, registry, etc.

I love Avast.