Ad Aware is a popular program used to remove "spyware" and "malware" from your computer, which are essentially non-propagative viruses. They install themselves on your computer and often resist removal. Most spyware reports your internet habits to somewhere else for, well, who knows. Some spyware can sniff your computer for credit card and personal information, as well as monitor passwords.
Ad Aware can be downloaded at
http://www.lavasoftusa.com/support/download/This program can remove most (but currently not all) forms of spyware found on your computer. Follow its operation instructions. Some things cannot be removed until your computer is rebooted and Ad-Aware is run again on startup. Even then, sometimes programs still cannot be removed. In this instance, do internet searches for the filenames, and look for instructions for removal. Remember to update Ad Aware frequently.
Spybot Search & Destroy is a similar program that does precisely what the name implies it does. Sometimes it catches things Ad Aware doesn't. However, some users report that Spybot S&D identifies important parts of your computer as spyware, and deleting them can cause havoc to your operating system. Some users deny this. Use it at your own risk.
Spybot Search & Destroy can be downloaded at
http://www.safer-networking.org/en/download/Spyware gets on your computer through surreptitious downloads caused by visiting what otherwise seem to be normal websites. It exploits features in Internet Explorer that run certain ActiveX controls without asking for permission. The best way to prevent getting spyware in the future is to use a web browser that isn't Internet Explorer or uses the IE libraries (like the internal AOL browser). Browsers like Mozilla, Firefox, Netscape, and Opera don't suffer from the same ActiveX faults as Internet Explorer.
If you still want to use Internet Explorer, I recommend opening the "Internet Options" menu item in your browser, and changing some of the security settings. There will be a window detailing permissions for ActiveX controls. You should set most of these to "prompt", so whenever a website wants to run an ActiveX script, you have control.
Mozilla and Mozilla Firefox can be located at
http://www.mozilla.org/Netscape, a product based on Mozilla, can be located at
http://channels.netscape.com/ns/browsers/default.jspOpera, a non-free product, can be located at
http://www.opera.com/The Google Toolbar for popup-blocking in IE can be located at
http://toolbar.google.com/