Mal-Ware programs are getting to be more and more invasive.
You can try an on-line scan such as the one offered by Zone Labs.
www.zonelabs.com
Hijack This:
http://www.spywareinfo.com/~merijn/downloads.html
If you are running Windows 98 or XP, you can use msconfig to more closely check what programs run at startup.
You can also use task manager (Ctrl-Alt-Del) to see what is running. You need to look at running processes, not just programs.
Clean out your temporary Internet files and cookies.
Once you have your system cleaned, you need to do a few things:
1. Tighten ALL browser security settings.
At a minimum, you want to be prompted for ALL ActiveX controls and software installations.
2. Install a pop-up blocker, or use Mozilla or Firefox in place of IE.
www.mozilla.org
3. Even for dial-up, I recommend installing a software firewall such as Zone Alarm.
www.zonelabs.com
4. Disable image preview, or better yet the preview pane on your email client.
Chas