Chapter 1. How the Internet Works

The very thing that makes the Internet such an open place, and a great way to communicate with the world and gather information, also makes it easy to attack your computer and potentially invade your privacy. The Internet's open communications protocols make the security dangers possible.

These protocols do something very simple. They break up every piece of information and message into pieces called packets, deliver those packets to the proper destinations, and then reassemble the packets into their original form after they've been delivered so the receiving computer can view and use them. Two protocols do thisthe Transmission Control Protocol (TCP) and the Internet Protocol (IP). They are frequently referred to as TCP/IP. TCP breaks down and reassembles the packets, and IP is responsible for ensuring the packets are sent to the right destination.

TCP/IP is used because the Internet is what is known as a packet-switched network. In a packet-switched network, there is no single, unbroken connection between sender and receiver. Instead, when information is sent, it is broken into small packets, sent over many routes at the same time, and then reassembled at the receiving end. By contrast, the telephone system is a circuit-switched network. In a circuit-switched network, after a connection is made (as with a telephone call, for example), that part of the network is dedicated only to that single connection for a finite period of time.

The Web uses these protocols, and others, as a way to deliver web pages and other information to your PC. It works on a client/server model. The client is your web browser; the server is a web server that delivers pages to you.

Why do these protocols make the Internet such an unsafe place? Because they were designed for openness and simplicity, so the packets that are sent back and forth over email and over the Web are open to inspection by anyone with a little bit of technical know-how. All someone needs is a piece of free software and a bit of knowledge, and he can examine the packets. Additionally, the various Internet protocols make it easy for someone to hide his true identity or even pose as someone else.