Sometimes it seems that you can never be safe on the Internet. You update your antivirus program, then read some story about the dangers of cookies or something. You download a ‘cookie crusher' utility, then find out about port scanning. And spyware. And all the scary things hackers can do too your system. It's amazing that anyone has the courage to go online at all.

Or at least it would be if all these things were actually true. Look more closely and you discover that many of these threats are exaggerations at best, and don't apply to most people. Learning to pick these out is very useful, because it enables you to concentrate on the real threats, and there are plenty of those.

Understanding which problems really are scary isn't the end of the matter, though – you need to know where to go for help. Unfortunately, there are plenty of sites with misleading security information, or others trying to sell you protection software based on promises that simply cannot be true. Picking fact from fiction can be difficult, so what should you do?

Networking Basics

All computers on the Internet have a unique IP address, represented by four numbers between 0 and 255 and separated by periods – for example, 217.46.129.21. When you enter a URL in your browser, it must be translated to an IP address before you can reach the site. It's not only big websites that have IP addresses, of course – you have one too. Whenever your browser requests a page from a website, it also tells that site what your IP address is, so the site can send the information back to you.

There's more to Internet identities than IP addresses. Let's take a web server as an example; as well as letting you view web pages, it might have FTP server software running so that you can browse for files to download. The same computer might even function as a mail server, sending and receiving messages. Information relating to any of these functions can arrive at any time – receiving a web page request right in the middle of being sent a large email, for example. So, how do you keep them organized?

The answer is ports (a port doesn't refer to a physical connection, like the serial port on your PC – it's purely a virtual thing). When your browser sends a command to a web server, it will use the default http port 80, while FTP commands go to port 21. On the server, each program is said to be ‘listening' to a particular port only, and will ignore commands from anywhere else.

Once again, this scheme applies just as much to the humble home based PC or Mac as a big web server. Both have these ports, and both may be giving out more information than you realize – unless you know how to close them down.

The Risks

Are you really at risk by other Internet computers using your IP address and ports? One measure of protection is provided by the way IP addresses are typically allocated. If you use a standard modem connection to dial up your ISP over a normal telephone line then you'll find most ISPs give you a different IP address every time you connect, making it very difficult for anyone to target you specifically.

On the other hand, anyone with an ‘always on' connection, perhaps via ADSL or a cable modem may have one IP address which stays the same (for a while anyway). And with the existence of programs called port scanners that can quickly check thousands of IP addresses for unsecured PCs, going online has to involve some level of risk, doesn't it?

Well, it depends on how your system is set up. Don't forget that while you can browse a web or FTP server freely; it's because that computer is running special software to make it possible, and PCs aren't set up this way by default.