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Chapter 21. Implementing Windows Vista’s... > Windows Firewall: Bidirectional Prot...

Windows Firewall: Bidirectional Protection

If you access the Internet using a broadband—cable modem or DSL—service, chances are, you have an always-on connection, which means there’s a much greater chance that a malicious hacker could find your computer and have his way with it. You might think that with millions of people connected to the Internet at any given moment, there would be little chance of a “script kiddy” finding you in the herd. Unfortunately, one of the most common weapons in a black-hat hacker’s arsenal is a program that runs through millions of IP addresses automatically, looking for live connections. The fact that many cable systems and some DSL systems use IP addresses in a narrow range compounds the problem by making it easier to find always-on connections.

When a cracker finds your address, he has many avenues from which to access your computer. Specifically, your connection uses many different ports for sending and receiving data. For example, the File Transfer Protocol (FTP) uses ports 20 and 21, web data and commands typically use port 80, email uses ports 25 and 110, the domain name system (DNS) uses port 53, and so on. In all, there are dozens of these ports, and every one is an opening through which a clever cracker can gain access to your computer.


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