Symantec needs to read some tutorials

Interesting related story from article pointed by MrAnonymous:
Does anybody like Norton AntiVirus? and this pragraph:
"So the situation right now is that Norton AntiVirus 2005 ?which costs more than AU$90 from Symantec�s Web site and is labelled "The world's most trusted antivirus solution" -- can be fooled by a simple script into turning off its auto-protect functionality and leaving the computer at a malicious user's mercy."

I'm using Kaspersky and it is fine but the problem is that it slows down the computer big time...ingoring the fact that on it took 3 hours to perform a full system scan on 2 drives.

Does anybody here have expirience with good anti vir/trojan tool that will work in background and be almost "invisible".

10x to all suggestion in advance