I've been playing the free software game for years. I've tried most of what's already been mentioned, but kept having issues. I'd be good for so many months, but then something would start happening to my computer. I'd search for it and not find it. I'd update the software, and some programs automatically updated every day anyway, but nothing would catch the problem. Twice I've had to take my computer in to have it done by pros. I asked them what they used and what they recomend, and they said the same stuff that I already had. I sometimes wonder if they just say that so they don't have to give up their secret software that actually works.
I was hit a few months ago, and before bringing it in again, I did a search for programs that I could buy that actually worked. Over and over again, I came up with Spyware Doctor by PC Tools. The review sites and PC magazines all rated it as the best out there with a very good support team and updates. One of the problems that the free stuff and even the other bigger names products lack is good updates when something new comes along.
I bought it and after installing it, found the problem. It fixed it and my system was back to working like new. I then went through and deleted every other program tha was on my computer that was supposed to do what Spyware Doctor accomplished.
It allows you to run it on three computers, so I gave it to my wife to run on her laptop. She wasn't having any issues, but wanted to install it just to be safe. She found hundreds of things on her system. After fixing it, she's found that her computer is running allot faster, and without any problems that she thought was just part of the way her computer worked.
To get what works, I think you have to spend the money on what really works.
Eddie