Our examination of computer viruses leads us to the conclusion that they are very close to what we might define as "artificial life." Rather than representing a scientific achievement, this probably represents a flaw in our definition.
"Computer Viruses: A Form of Artificial Life?" (invited contribution); Artificial Life II, Studies in the Sciences of Complexity, vol. XII, eds. D. Farmer, C. Langton, S. Rasmussen, and C. Taylor; Addison-Wesley; pp. 727–747; 1991.