Selective targeting (or targeted killing) of terrorist leaders is a legitimate mode of operation and part of a state's counterterrorism, anticipatory, self-defense activities that are designed to prevent the continuation of terrorism. Paradoxically, this counterterrorism measure is the best way of preserving the military ethical conventions of “purity of arms.” The concept refers to moral rules advocating the exercise of restraint and compassion in the course of a confrontation with the enemy. The “purity of arms” concept is debated extensively in democracies. Selective targeting of terrorist activists is a measure designed to hurt the real enemy while minimizing civilian casualties. Terrorist leaders and planners are targeted and an attempt is made, trying to avoid so far as possible, “collateral damage” that often accompanies any general military offensive. Customary international law permits targeting the enemy, provided that the criteria of necessity and proportionality of the attack are maintained. The relationship between the threat of terrorist attacks and the actual attacks carried out is shown in this study. The results contribute to reinforcing the legality of selective targeting as a preemptive mode of operation because they show that one should relate to a threat of an attack as to an imminent danger.