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Chapter 7. Networking and Internetworking > Securing Your System on a Network

7.3. Securing Your System on a Network

Security is a very real concern for any computer connected to a network or the Internet. There are three main categories of security threats:

A deliberate, targeted attack through your network connection

Ironically, this is the type of attack most people fear, but realistically, it is the least likely to occur, at least where home and small office networks are concerned. It's possible for a so-called hacker to obtain access to your computer, either through your Internet connection or from another computer on your local network; it's just not terribly likely that such a hacker will bother.

An automated invasion by a virus, robot, or Trojan horse

A virus is simply a computer program that is designed to duplicate itself with the purpose of infecting as many computers as possible. If your computer is infected by a virus, it may use your network connection to infect other computers; likewise, if another computer on your network is infected, your computer is vulnerable to infection. The same goes for Internet connections, although the method of transport in this case is typically an infected email message.

There also exist so-called robots, programs that are designed to scan large groups of IP addresses, looking for vulnerabilities. The motive for such a program can be anything from exploitation of credit card numbers or other sensitive information to the hijacking of computers for the purpose of distributing spam, viruses, or extreme right-wing propoganda.

Finally, a Trojan horse is a program that works somewhat like a virus, except that its specific purpose is to create vulnerabilities in your computer that can subsequently be exploited by a hacker or robot. For example, a program might open a port on your computer (see Appendix D) and then communicate with a remote system to announce its presence.

A deliberate attack by a person sitting at your computer

A person who sits down at your computer can easily gain access to sensitive information, including your documents, email, and even various passwords stored by your web browser. An intruder can be anyone, from the person who steals your computer to a co-worker casually walking by your unattended desk. Naturally, it's up to you to determine the actual likelihood of such a threat and to take the appropriate measures. Such measures are discussed in Chapter 8.



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