Tech-Planets : Protecting Your Computer from Unwelcome Intruders

These days, practically everyone's online, downloading and exchanging files, and developers are in such a hurry to get their Web sites up or their files out that checking for a nasty bug is more of a courtesy than a requirement. If you're not careful, your computer can end up with a nasty virus that makes your files act oddly, crashes your computer, pops up bizarre messages, or worst of all, destroys your operating system.
A computer virus is the most subtle of computer problems. It usually loads itself into your computer system when you run a program to which it has attached itself. From the computer system, it'll then reproduce itself, much like a biological virus would, by attaching copies of itself to other programs on your hard drive. What it does then depends on the malevolence of its creator. Some viruses are nothing more than a practical joke. They may bring up a message like "Merry Xmas" or melt your display. Most of them though, either start destroying your system or your files immediately or on a date specified by their creators—like the much-publicized Michelangelo virus, which erases important pieces of your system on March 6. "Trojan horse" programs are similar to viruses in their effect on your system, but they can't reproduce themselves. They're usually a program disguised as something you might want to download onto your computer—for instance, a rogue, modified version of PKWare's PKZIP utility. But when you run the new program you just found, it can do anything from popping up a message to erasing your hard disk, as the rogue PKZIP utility really did.
In either case, you have to actually launch the infected program or the trojan horse for it to infiltrate your system. Though hoax e-mails, like the one about the "Good Times" virus try to make you believe otherwise, neither a virus nor a trojan horse rogram can do anything if you simply leave the malevolent file sitting on your hard drive.
Finding out that you copied a trojan horse onto your computer is remarkably easy. You launch the program, and the next thing you know, something completely unexpected happens—maybe your system is gone or your computer is laughing maniacally at you. But unless you notice your computer acting oddly before the virus has done its worst damage, you may very well not know you have it until it's too late.
If your computer is not on a network, and you never, ever install new programs or download files from the Internet or open email enclosures, you don't have to worry about viruses. But that's like living in a sealed bubble. Most of us have to go out into public every day, where we're subject to the germs carried by others (though natural immunities will usually protect us from most of them.) Likewise, most people also have to update their software and are interested in communication and information from others. Luckily, there are some preventions and cures for even the nastiest of viruses.