I use a massive combination of tools and utilities. Just to name a few of the more readily available:

AVG, Ccleaner, Clamwin, Malwarebytes, Spybot Search & Destroy w/Teatimer and resident protection scripts, Superantispyware, Peerguardian 2 (with custom blocklists), Zonealarm Firewall only, Hackthis, a pack of rabid wolverines, and the bone dust of a 300 year old juju priest for good measure.

Personally, having done many system and virus cleans both freelance and for a shop I have absolutely no respect for Norton, or any symantec product, Microsoft firewall, or most Mcafee products - the most heavily infected systems I had to clean always had one or more of them running and were sure they were safe from virii.  AVG is not as good as it used to be, but I personally am not fond of Avast because of the constant need to reverify to keep the free key working - free should be hassle free too.  I have heard many people like kaspersky, but have no feelings either way about it.

Also, the minute my PC does anything... ANYTHING out of the ordinary or unusual, I promptly disconnect the internet connection and begin scanning the crap out of it. I also have a bootable USB with a number of virus solutions on it that I periodicly update definitions on, just in case.

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