What Are They?

Understanding Computer Viruses:

An Overview

The first viruses emerged in the mid-1980's. By 1990, there were still less than 100 viruses. Today it is estimated that there may be more than 50,000 viruses. Interestingly, the majority of viruses are not out in the public, referred to as "in the wild." Resources say that only 100-180 of the 50,000 viruses account for all the viruses that are in the wild. Most of the viruses exist only in personal virus collections, also called “virus zoos.”

A computer virus is simply a computer program. It is intentionally written so that it will spread by creating copies of itself and attaching the copies to other files. Any program that does this is considered a virus. Viruses generally reproduce without the user's knowledge or permission. Viruses are written with the intent of damaging other computers or annoying other users. They can be written by anyone with programming knowledge.

Most viruses have two phases to their existence, the infection phase and the attack phase. All viruses have an infection phase, but not all have an attack phase.

During the infection phase, the virus spreads itself. If a virus infects too fast, it is usually easy for anti-virus programs to spot. Therefore many try to be subtle about it.

Viruses can be spread by innocent people that are just doing their daily routine. Infected files can be spread in the following ways: by diskettes, networks, bulletin boards, or e-mail attachments. Infected files can be stored on servers, floppy disks, hard drives, and CDs. Infected files can even be found on new hardware or software.

Example: File Virus Infection Phase

"Your friend gives you a game on a disk. The game has an infected file that you don't know about. Each time you play the game, the virus copies itself into another program without you knowing. Now, whenever either of the programs are executed, the virus is copied. This continues as the virus infects the rest of the computer. If any of the files are transferred to a floppy disk or e-mail attachment, and they are put on another computer, the process starts again"

On viruses that do have an attack phase, the attack phase is set off by a trigger, such as a time or date. The attack phase is when the virus causes damage or other unwanted system behavior. In order to made sure it has spread, viruses often delay the attack phase, sometimes for years.

The attack phase has a wide range of severity. Although all viruses take up space and use system resources, some do little more damage. Some viruses display messages but then others can crash your hard drive completely. They can even corrupt your backup files if you're not careful.

Although there are over 50,000 viruses, most resources report that 80 - 95% of them do little damage to a computer other than cause annoyances and take up system resources such as disk space and memory. By using up system resources, even an otherwise non-damaging virus can slow the computer and reduce its efficiency.