As previously noted (p. 1.3:47), borderline cases—such as viruses in the case of the concept life—do not invalidate a concept. The conclusion that "self-sustaining and self-generated action" is what essentially distinguishes life from non-life is supported by our view of viruses. The latter are seen as lifelike in their capacity for self-replication, yet more akin to inorganic chemical molecules in their dependence upon cellular processes of true organisms for their survival. Even computer viruses are often described in biological metaphors, reflecting their analogous powers of self-generation. These artificial "organisms," however, are utterly dependent upon man-made hardware and software for their existence—a requirement often conveniently overlooked in movie scripts designed for popular consumption.