Quote from palinuro:
Lavasoft found 1 trojan on my computer, but didn't find the last one I had--that was caught by SpyBot (highly recommended, not just by me). I also use SpywareBlaster as a guard. Plus a standard antivirus program. And I run Hijackthis periodically just to see if anything looks suspicious.
The point is, you may need to run lots of them to find the problem.
