Norman Book on Computer Viruses
What is a virus?
The terms “computer virus” and “virus” are used very loosely in everyday conversation and have become synonymous with “trouble”.
A virus is usually not something that creates cool screen effects and enables you to hack into Pentagon. The “Launching virus” screen as seen in Hollywood movies bear no resemblance with real life viruses. In reality, a virus infection is most often invisible to the user. The machine may slow down a little. Some programs may be unstable and crash at irregular intervals, but then again that happens ever so often on clean systems too.
Still, some viruses have some sort of screen effect. The Windows virus “Marburg” fills the desktop with red circles with a white “X” inside”. A couple of viruses will make desktop icons escape the mouse cursor. Such effects are not particularly common, since they expose the existence of the virus. In order to explain such vexing programs, we will need to look at what programs really are.
What is a program
A program is a recipe for a computer’s behavior. Now, computers do not read these things as we humans do. They cannot understand free text messages – instead they have to rely on numbers, because computers are really only glorified calculators. For example, let’s look at the instruction for “do nothing” in ordinary Intel processors (yes, there is an instruction for that) – it’s the number 144. If the number 144 is translated into binary it can be written as 10010000 – which physically means voltage on, off, off, on, off, off, off, off in wires going into the processor.
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