“ In all things of nature there is something of the marvelous.”
One of the most important steps toward understanding computer viruses is learning about the particular execution environments in which they operate. In theory, for any given sequence of symbols we could define an environment in which that sequence could replicate itself. In practice, we need to be able to find the environment in which the sequence of symbols operates and prove that it uses code explicitly to make copies of itself and does so recursively1.
A successful penetration of the system by viral code occurs only if the various dependencies of malicious code match a potential environment. Figure 3.1 is an imperfect illustration ...