If your computer sits in an office shared with others or if your family computes together, there's a risk someone will get interested in what you're up to. Some of those things – tracking financial information, your secret diary, your Christmas purchases – you may not wish to share.
With the threats from viruses and spyware, it's all too easy to forget that some of the biggest threats to your privacy and security are posed by people who can physically get their hands on your computer.
Zombies and DoS
If you've read this far and are thinking "I'm safe – there's nothing on my computer except a bunch of games," have another think. There are people out there who couldn't care less about the information stored on your computer, but they are certainly interested in your computer itself.
Spammers, hackers and virus writers have a vested interest in keeping their identity secret. To stay hidden, one tactic they use is to find unprotected computers on the Internet and use those computers to launch attacks or send spam. Your humble Internet-connected home PC is thus a valuable pawn in their schemes.
Hackers use a piece of code called an agent or daemon to control remote PCs without the owner's knowledge. They then use one or thousands of controlled PCs, known as zombies, to launch attacks on juicier targets. Zombie PCs are crucial in Denial of Service (DoS) attacks, designed to bring the Internet or a part of it to a standstill.
As well as hackers, spammers may find your computer a useful way station. Some spammers seek out vulnerable PCs and, when they find one, install a complete email server on it. They then use this hidden mail server to deliver tens of thousands of spams.
