Are you using the free version of Ad-Aware? It's more for finding spyware & adware. Do you have an antivirus program??
Have a look through through the thread below, it has info about some free AVs (I use AVG's free version).
http://www.gnutellaforums.com/showthread.php?t=58603

If you end up at Norbie's site for computer help, he also has a good section for downloading antivirus, antispyware etc.