If you have a Windows NT, 2000, XP or 2003 machine that you use to connect to the Internet, chances are that at some point you have installed IIS (Internet Information Server) - microsoft's web server. Most people use IIS as a local intranet for sharing company information.

By default IIS will serve web pages on all it's network connections. Even dial-up ones. This means that potentially a hacker could read your private intranet pages, or exploit loopholes in IIS to launch virus attacks or destroy files.