10.2. What Is a Virus?
The precise definition of a virus has been hotly debated for many years. Experts have had difficulty describing the specific traits that characterize a true virus and separate it from other types of programs. To add to the confusion, people tend to lump viruses, worms, Trojan horses, and so on under the generic umbrella of "virus." This tendency is partly because no one industry-acceptable descriptor includes all these program types. Confusion continues over exactly what constitutes a virus.
The generally accepted definition of a virus is a program that can be broken into three functional parts:
The combination of these three attributes makes the collective program a virus.