What is a Computer Virus?
A computer virus is a program that requires a host in order to make copies of itself on computer disks. Viruses may infect (copy to, and spread from), program files, programs in disk sectors, and files that use macros. The ability to self-replicate distinguishes viruses from programs that do not, and this parasitic nature is neither an accident, nor a computer glitch. All viruses are created by people who know how to write computer programs.

Why are they called Viruses?
The first theories about the possibility of creating a self-replicating program date back to 1949, and experimental viruses were first programmed and tested in the 1960s. They got their name when a university professor used the term "virus" to describe them 1984, because like a biological virus, a computer virus is small, makes copies of itself, and cannot exist without a host. When personal computers became popular, PC viruses began to appear (in 1986-1987), at first intended as jokes, or developed for research or demonstration purposes.

What is a Computer Worm?
As intranets and the Internet have grown in popularity, e-mail has evolved from a convenience to a necessity. Virus vandals know that, and they've invented new ways to use e-mail to spread viruses, and especially, worms. A worm program is similar to a virus. It is considered by some to be a subset of a virus in that it makes copies of itself but does so without needing to modify a host. Like viruses, worms may (or may not) do things other than replicate.

What is a Trojan horse?
Trojan horse programs are named for the giant wooden horse that concealed Greek soldiers who used it to invade the ancient city of Troy. Like that famous trick, a Trojan horse program conceals hidden programming. The hidden function may just be a joke, or something annoying, but vandals often use Trojan horse programs to destroy other people's data, knowing that some people will run any program that has an interesting file name, or promises to perform a useful function.

Are all these programs harmful?
They waste disk space and memory, delay computer operations, and increase the likelihood of system crashes. They are often poorly written and may function erratically, overwrite data, and cause programs to run erratically. Many also have destructive routines to alter or overwrite data. In addition, the cost of antivirus software and the time recovering from virus damage is passed along to consumers by businesses at the cash register.

Who creates these programs - and why?
Virus writers range from researchers, to pranksters, to malicious vandals. The typical virus writer is an otherwise intelligent male, between 15 and 23 years old. He may be bored, curious, or intent on doing forbidden things, just to frighten others. Some belong to organized virus-writing groups (usually short-lived), and those in the group often respond to peer pressure, trying to outdo the others. Whether in a group or not, some get satisfaction from the challenge, while others think of themselves as rebels against the "system."

How do they spread?
Viruses and Trojans spread from one computer to another by using one or more methods, all of which depend on user carelessness. Some people never have a problem, but others who are not as careful (or lucky) infect their hard disk by running downloaded files, or after placing a newly-obtained floppy disk in a drive. Viruses and worms spread fastest among computers networked on a LAN, especially when e-mail file attachments are involved.

Is sharing files a problem?
Sharing certain types of files with others always involves some certain risk. The medium is irrelevant; files from a LAN server, downloaded from Internet sites, from a floppy (even from shrink-wrapped software). Riskiest of all are files posted on Internet newsgroups, because there is no control or accountability. Many people have become the first victims of brand-new viruses and worms, by downloading executable files that were posted deliberately by vandals.

What about e-mail?
Before the growth of the Internet, viruses used to spread more slowly, from user to user, and anti-virus vendors were usually able to distribute a remedy before things got out of hand. That's all changed, especially with worms, because some people will click on any e-mailed file that they receive. Vandals have seized their opportunity, and created programs designed to spread to all those who correspond with careless users. Because of this threat, the only 100 percent safe e-mail file attachment is a deleted e-mail file attachment.

Can a cookie contain a virus?
Some Web sites store information on your computer, in small text files called cookies, that can be used when you re-visit that site. Examples include items you've selected for purchase, registration data, or your user name and password, for Web sites that require them. Since cookies are text files, they are not executable, and this fact eliminates the possibility of viruses, because they must be hosted by an executable file. It is theoretically possible to include UUencoded or MIME comments, but decoding a UUencoded or MIME file and executing it is not possible.

Do you need to worry?
Worrying will get you nowhere. Instead, take sensible precautions, to avoid losing data should you be affected by a program that was designed to cause problems. Many people are fortunate never to encounter one, but a vandal's program could be concealed in the next file you download, or in a file attached to an e-mail message. Or the threat could be on the next floppy you insert in a disk drive, especially one obtained from a friend, a co-worker, or a fellow student.

How can you tell whether your computer is infected?
Because some viruses cause strange things to happen, an odd or unexplained event may lead a user to conclude a virus must be responsible, without bothering to explore other possible causes. On the other hand, many viruses are carefully programmed to do nothing to betray their presence. The solution to this dilemma is not to assume anything, but to rely upon anti-virus software as a diagnostic tool.

How can you protect your data?
If you have files you can't afford to lose, make sure you have more than one copy of them. Programs may already be backed up on their original installation disks, but what about the files that you create? Business records, spreadsheets, manuscripts, and other important files can be lost in an instant to a virus, or to other causes, hard disk failure among them. If no other copy of your files exists, make copies of them, before it's too late.