How Computer Viruses Work

How computer viruses work

Computer viruses are not understood very well, but they get your attention. Viruses show us how vulnerable we are, but they also show how open and worldly human beings have become. Microsoft and other large companies had to shut down all their e-mail systems when the "Melissa" virus became a worldwide event.

A computer virus is passed on from one computer to another computer. A virus must ride on top of some other program to document in order to perform an instruction. After it is running, it can then infect other programs.

Viruses were first seen in the late 1980s; the first factor was the spread of personal computers. Before the 1980's home computers were non-existent or they were used for toys, and the real computers were very rare and they were locked away to only be used by the "experts."

The second factor was the se of the "bulletin boards"; any one could get to a bulletin board if they had a modem and download programs. Bulletin boards led to the precursor of the virus known as the Trojan Horse. It is a program that sounds really cool when you read it, so then people download it, and when people run the program, however, it does something uncool like erasing your disk, so people think that they are getting something neat, but it wipes out their system.

The third factor to viruses is the floppy disk. Programs were small and they could fit the operating system, or a word processor onto the floppy disk, and then turn on the machine and it would load the operating system and everything else off the disk. Viruses took advantage of these three facts to create the first self-replicating programs!

Early viruses were pieces of code attached to programs like games or word processors. People could download an infected game from a bulletin board and run it, and a virus like this is a small piece of code embedded in a larger, legitimate program. The virus loads its self to memory and looks around to see if it can find any programs on the hard disk. When it finds one it modifies it to the virus's code to the program. Then the virus launches the "real program," and the user has no way of knowing that it is infected. The next time this program is executed, they infect other programs, and the cycle continues.

The spreading part is the "infection" phase of the virus, and it would not be so violently despised if all it did was replicate themselves. Some viruses might print silly messages on the screen to erase all of your data, and the trigger might be a specific date, or the number of times the virus has been replicated, or something like that.

The other trick to replicate themselves is to infect the boot sector on the floppy disk and the hard disks. The boot sector is a small program that is the first part of the operating system that the computer loads, and it contains tiny programs that tell the computer how to load the rest of the operating system. By the virus putting its code on the boot it can guarantee that it gets executed and loads itself into the memory and is able to run whenever the computer is on.

Executable and boot sector viruses are not as threatening as they were before because the decline in the huge size of today's programs. Almost every program people buy today comes on a compact disc, and they cannot be modified which makes the viral infection of a CD impossible. Boot sector viruses have declined because operating systems now protect the boot sector. Both are still possible, but now they don't spread as fast as they once did.

The newest virus is called macro virus and Melissa virus. Melissa was created