Hello. A word about antivirus software. There is a very good reason why some antivirus apps are CPU hogs and others aren't. Antivirus software is supposed to scan files for viruses. This scanning is an application like every other app, with a big difference: AV 'touches' every file, scans it and releases it. It is completely normal that this action slows your machine down, I'd say it's abnormal if it doesn't. But your machine has to stay workable, of course. If it's getting too slow when AV is running, you should consider buying a new pc...
Some antivirus manufacturers choose to scan for all possible viruses, others choose to scan for generic viruses or for virus families. The latter slows your pc down less than the former, but in my opinion the first is more secure (my experience has proven me right on this one).
And to call names: though they're not the cheapest, Norton and McAfee are still the most popular AV choices, and there's a good reason for that.
I would NEVER install some free AV on my pc.
