Recently, active worms have done significant damage due to their rapid propagation over the Internet. We studied propagation mechanisms of active worms employing single target discovery technique and various combinations of two or three different target discovery techniques from attackers’ perspective. We performed a series of simulation experiments to investigate their propagation characteristics under various scenarios. We found uniform scanning to be an indispensable elementary target discovery technique of active worms. Our major contributions in this paper are first, we proposed the discrete time deterministic Compensation Factor Adjusted Propagation (CFAP) model of active worms; and second, we suggested the combination of target discovery techniques that can best accelerate propagation of active worms discovered from results of the comprehensive simulations. The significance of this paper lies in it being very beneficial to understanding of propagation mechanisms of active worms, and thus building effective and efficient defense systems against their propagation.