You’ve probably already heard a lot about viruses and the potential harm they can cause. The stories can be downright scary. It’s important to remember that a computer virus is nothing like a human virus.

A computer virus is just a program that runs on your computer, like any other software. If you’re properly prepared, you can detect and remove many viruses fairly quickly and painlessly. What Can a Virus Do? A virus is a program designed to automatically migrate to other computers, and it can do so without any user interaction.

Most viruses also carry a payload, which is a separate set of instructions, typically designed to cause some kind of harm, such as:

• Format your hard disk, which will result in the destruction of all data and programs on the hard disk.
• Place random messages on your screen, just to be annoying.
• Delete random files from your hard disk.
• Send random files from your hard disk to random people in your address book, by using your e-mail program, without your knowledge.
• Send itself to everyone in your address book, by using your e-mail program without your knowledge.

These are only a few examples of the potential harm a virus can cause. Not all viruses have payloads. Some viruses do nothing at all. In April 1994, there were 3,000 known viruses.

In May 1996, that figure grew to 9,000. Today, there are more than 58,000 catalogued viruses, with 10 to 15 new viruses discovered each and every day.

To have a computer without antivirus software installed is not just risky—it’s practically a guarantee that your computer will be (or currently is) infected.

It’s imperative that you update your antivirus software constantly in an effort to keep yourself protected from the most recent viruses.

How Does Antivirus Software Work?

In order for antivirus software to work effectively, it must be told how to recognize a particular virus. Consider how many post offices across the United States contain posters with pictures of the FBI’s “most-wanted” criminals.

The idea here is that if you recognize the person in the photo, you’ll contact the FBI. If the posters were never updated, the information would become obsolete over time.

In much the same way, antivirus software must be kept up-to-date with the equivalent of digital fingerprints of the most recently discovered viruses, while at the same time still remembering all the viruses of the past.

Since viruses never die or become extinct, the list can only grow larger. If your antivirus hasn’t been updated recently (or ever!), your computer could be infected even now!

There are also Trojans and worms, which many people consider to be in the same category as a virus.

A Trojan is a program that appears useful, but inside lurks a nasty virus just waiting to be released. Remember the story of the Trojan horse? That’s the source of this nasty software’s name.

A worm is a program that is designed to replicate itself in as many places as possible: all over your hard disk, through your e-mail, across networks, on the Internet, and even on floppy disks. Worms never take a break, and they work extremely fast.

They can tie up networks and cause crashes. Have you ever tried to call a radio station to win a contest? Were you ever able to get through?

So many people dialing at once creates a never-ending busy signal. This is the equivalent of what a worm can do to a network, or even to the entire Internet.

What Kinds of Viruses Are There?

Different kinds of viruses have different kinds of effects on your computer. These are the main types of viruses currently being distributed:

• Boot virus This kind of virus infects the very beginning of the hard disk. It’s the first thing the computer sees when you turn it on, even before the Windows screen appears. Boot viruses can be some of the most difficult viruses to remove.
• File infector virus This kind of virus attaches itself to certain types of files across your hard disk. When you run that file, it activates the virus.
• Macro virus This kind of virus attacks only applications—like Microsoft Word, Excel, PowerPoint, Access, Lotus AmiPro, and so on. It is typically harmless, causing problems that are usually just annoying and frustrating. The virus activates only when the application it’s associated with is in use.
• W32 virus This kind of virus infects Windows programs such as Notepad, Solitaire (gasp!), and even your screensaver.
• Script virus This kind of virus is often transferred by e-mail and is actually embedded into the e-mail itself (like a tick on a dog). Sometimes, just opening the e-mail to read it can cause your machine to become infected.
• Multipartite virus This type of virus is a combination, typically, of a boot virus and a file infector virus. You get two for the price of one!
• Mutation or polymorphic virus This kind of virus can be any of the viruses mentioned above, but it also attempts to elude detection by changing its structure. Every time the virus starts, one of the first things it does is change its “fingerprint.” Think of it as the chameleon of viruses.

Reading about all of these different types of viruses may make you nervous. But don’t worry; with current antivirus software, you can protect yourself from all viruses.