A virus in nature is a tiny organism that literally hovers at the edge of the living and the non-living. If it infects a host, it comes alive, using the host's resources to rapidly make many copies of itself, while possibly causing harm to the host. (There are some viruses that do no harm, or which might even benefit the host, living in a symbiotic relationship.) If it is not in a host and is left by itself, it is completely inert, consuming no resources and performing no actions indicative of life. In much the same way, a computer virus is a software program that is capable of infecting a host machine, and then making copies of itself while doing harm to the host.

Computer viruses have to be executable program code, and cannot be inert files that do not cause the computer to act. There are several...