Best thing I ever did was get rid of NAV. I don't know how to explain it in technical terms as I am not a techie, but it slowed the computer, seemed to take forever to do a scan, was just slow and cumbersome always was in conflict with other bits of software and was feckin expensive to add insult to injury.
The best advice I ever got was from E-Liams personal website. (he's one of the the fairly knowledgeable advisors on this board) Since following the instructions on there, I have never had a problem with a Virus, Worm, Adware, Malware etc etc. In fact when I use spybot these days it usually never even finds anything. I find AVG and Spyguard especially funky. Spyguard seems to block things before they even get a chance to get on your computer.
Set yourself free, get rid of NAV.
Heres the link:
Link
Its the Second Post down.