by Eric Lannak

Created on: February 05, 2011

Most computer users have heard of computer viruses, and are aware they shouldn’t open unknown email attachments or share removable memory (like disks and USB flash drives). We know these things can get into our computer, multiply there, and can cause problems like sluggishness, corrupted files, and hard drive erasure. But the viruses themselves are a bit of a mystery.

What are they? How do they work? To answer these questions we need to take a closer look at computer programs and how viruses came to be written.

PROGRAM VS CODE

A computer program is like a very involved recipe. It states the values and resources needed (like the “ingredients” section) and then instructs the computer to perform structured, step-by-step processes. Each individual step is written in a computer language or “code” like Unix, Visual Basic, or even assembly language (the most painstaking and fundamental code of all).

In the 1960’s, when computers were much simpler, programming was done by scientists and mathematicians. Programmers would sometimes compete to see who could devise the program that could most quickly replicate itself until it took over a computer’s memory. Eventually these programs (the first “worms”) became so small and effective that some speculated they could be a risk to computer security.

VIRUSES

Viruses developed from the thinking behind these “core war” games, but with a twist. Instead of creating programs, viruses were bits of code inserted into other programs. When that program was run, the viruses would copy themselves into other files. Using the recipe comparison, a virus would be a line like “copy this line to another recipe”, and the dutiful cook would do it. Then, when that new dish was prepared, the cook would reach the “copy this line” instruction and faithfully reproduce it in yet another recipe.

This seems like it would be fairly harmless, and it can be. But most viruses contain other instructions as well.

MALICIOUS CONTENT

Using the recipe example, imagine if the instruction said “bake in a 400 degree oven for one hour, and copy this line to another recipe”.  As the line was copied from dish to dish, the dutiful cook who follows directions exactly would be producing rock-hard baked goods, jerky-like meat dishes, and countless other inedibles. In a computer, such damaging directions could lead to corrupted files, lost data, and malfunctioning programs.

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