First, make sure that you have all the latest critical updates installed. Check out Microsoft's Windows Update site.
Next, check the security settings in Internet Explorer. While in IE, open the Tools menu and select Internet Options. Then, click the Security tab. Click the Internet zone, and note the security level selected. If it's below medium, set it to medium (the default). If it's set to medium, set it to high. This will prevent your homepage from being hijacked, but will probably cause problems with some Web sites. You should add those Web sites to your list of trusted sites, available from the Security tab.
The other possibility is that an application installed on your computer is resetting your homepage. This can be quite difficult to find. Start by opening the Control Panel -> Add/Remove Programs and remove anything you don't need or don't recognize. If that doesn't fix the problem, search Google for the word "spyware" -- you can find tools to help you identify and remove the annoying application.
This was first published in October 2003