My first advice is to use a higher quality spyware program (I don't know how good Yahoo's package really is). Go to
http://www.download.com
and search for Ad-aware (Lavasoft). Update the latest files and run a full system scan. It's free to use, but you have to check for updates and start scans manually. You can pay for the luxury of running it as another background task, but I don't think it's necessary for you or most home users. Just remember to run regular scans, once every two or three weeks is enough.
Next question: Do you have an up to date anti-virus program? I have seen Norton find one of these programs on a relative's computer, but I don't have enough knowledge of the product to justify that you buy it. AVG supply a free but restricted anti-virus program, and I have been told it's pretty good if you don't want to pay. I use and prefer McAfee, but only because I know the product well. If you don't have anti-virus, get it YESTERDAY.