The problem of peak power estimation in CMOS circuits is essential for analyzing the reliability and performance of circuits at extreme conditions. The dynamic power dissipated is directly proportional to the switching activity (number of gate outputs that toggles (changes state)) in the circuit. The Power Virus problem involves finding input vectors that cause maximum dynamic power dissipation (maximum toggles) in circuits. As the power virus problem is NP-complete the gate-level techniques are less scalable with increasing design size and produce less optimal vectors. In this paper, an approach for power virus generation using behavioral models of digital circuits is presented. The proposed technique converts the given behavioral model automatically to an integer (word-level) constraint model and employs an integer constraint solver to generate the required power virus vectors. Experimenting the proposed technique on ISCAS behavioral level benchmark circuits and the standard DLX processor model show that the above technique is fast and yields higher-quality results than the known gate-level techniques. Interestingly, the paper attempts to generate an assembly program that cause the maximum dynamic power dissipation on the given DLX processor model. To the best of our knowledge the proposed technique is the first reported that considers power virus generation using behavioral level models. © 2007 IEEE.