Self-replicating malicious codes (worms) are striking the Internet vigorously. A particularly sophisticated recent introduction is the “killer” worm (also called counter-worm or “predator” worm). The goal of this research is to explore the interaction dynamics between a worm (prey) and an antagonistic worm (predator), using mathematical modeling. This research models several interesting combat scenarios of two fighting worms, including the effect of antivirus and system patches on the system behavior. There are few novel findings of our enhanced model, such as the prediction of oscillatory behavior of interacting worms population conforming to existing biological systems.