ugh.. NAV leaves something like 200+ traces in your system.. even after official removal. it also corrupted on me at least 2 or 3 times a year and required reinstallation.
3 years ago got nailed w/ a trojan that it let slip by. it could detect it but not clean it. after days of playing hide-and-seek with the trojan I gave up and was about to give to a computer geek buddy for further action. in the mean time I unloaded NAV (comp ran much faster!) and loaded AVG Free... which to my surprise, promptly found the trojan AND a 2nd one I was not yet aware of. A simple click and it was obliterated.
A free program did all that without pain. Havnt been infected since, and my computer runs noticably faster too.