Invasion of the Computer Viruses

Simply stated, a computer virus is a computer program written by a person (not always, but usually, a jerk) who designed it to spread to as many computers as possible.

This definition seems simple enough, but indulges me. I’d like to zero in a bit further, to clarify some issues and to dispel some misunderstandings:

Computer program: A virus is nothing more than a set of instructions, written in a high-level programming language, such as Visual Basic, C, C++, or Java, translated into “native” instructions (a long list of ones and zeros) that are used by the computer’s CPU.

Written: It’s worth repeating: Viruses don’t just happen; people write them deliberately.

Spread: This is the essential characteristic of viruses. They are designed to be mobile to move from computer to computer, either under their own accord, or as a “hitchhiker,” by attaching themselves to another computer program and then going wherever that computer program goes.

Most viruses also have a payload, the instructions that the virus performs in addition to its characteristic of spreading from computer to computer. Consider the payload as the virus’s bonus material. The payload is usually triggered by some event, such as a particular date, a particular time, or a double click that opens a particular file. The payload can range in behavior — from displaying silly messages on-screen to deleting important files, communicating your personal information to an unknown third party, or sending embarrassing e-mail messages in the name of the computer’s rightful user (or, often, some other innocent party that the virus has recently visited, or one found in the victim’s e-mail address book).

Trojan horses and worms share many similar characteristics with viruses, although they use slightly different ways to get from here to there.