21.1. Know Your Enemies The steps to safeguarding your computer make more sense when you understand the nature of the threats you're dealing with. Here's the Internet's Seven Most Wanted: -
Viruses . A virus is a nasty little piece of code (that is, a small program) that invades your computer without your knowledge. Like a flu bug that spreads from person to person, a virus can replicate itself and jump from computer to computer by attaching itself to a host file. If you unwittingly open the infected host filefor example, a song you download illegally or a file called "Britney Bikini Pic.jpg"the virus code leaps into action and starts doing its damage. Viruses can cause erratic computer behavior or even erase files on your hard drive. -
Worms . A member of the evil virus family, a worm also spreads by replicating itself over networked computers. But a worm doesn't need human involvement or even a host file to perform its nasty duty. Worms have caused entire office networks to crash, costing companies millions of dollars in damages and lost productivity. -
Trojan horses . Like the Greek myth it was named after, a Trojan horse is a deceptive file or program. It appears enticinga game, perhapsso you cheerfully install it on your hard drive. Once it's there, the software quietly gets down to business. Trojan horses can secretly transmit your passwords and account numbers to Internet criminals, or provide the means for someone to take over your computer. -
Spyware . Not as destructive as a virus but just as sneaky, spyware has become a huge problem around the Internet. A spyware program gathers information about you and your computing habits and then quietly transmits the information back to its spymasteroften an advertising or marketing company. -
Third-party cookies . Alongside the good cookies that let Web sites remember and automatically fill in your login information and other preferences, there are bad cookies. Called third-party or tracking cookies, they don't even originate from the Web sites you surf to. Instead, a company that advertises on that site slips its own cookies onto your computer to trace your movements as you roam the Web. -
Phishing . Those junk email messages clogging up your inbox are usually more of an annoyance than a threat. In the hands of sneaky identity thieves , though, email can be much more dangerous. Phishing refers to massemailed phony messages that trick people into handing over their passwords, credit card information, and even social security numbers. Just as the pronunciation implies, phishers sit back and wait for their victims to bite. -
Hijacking . You're the one who pays for the Internet connection and sits at the keyboard, so you're the only one who can control your computer, right? Wrong. That connection is a conduit both into and out of your machine. If you don't shield it properly with a firewall (Section 21.6.1), anyone with a bit of programming skill (and a lack of moral fiber) can pipe in programs and commands that take over your computer.
Note: Most of these maladies affect only Windows PCs. The Macintosh is largely unaffected by viruses, worms, spyware, and so on, partly because its smaller market share makes it a smaller target for the virus writers, and partly because it's a more modern, much more secure operating system to begin with.
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