Active Cyber Defense tend to be associated with the phrases “hacking back” or “attacking the attacker,” denoting retaliation or retribution with the likelihood of harming unrelated third parties. Nevertheless, Active Cyber Defense has long been employed by States facing increasingly sophisticated cyber incidents in combination with Passive Cyber Defense. Some of the Active Cyber Defense measures taken against another State in self-defense fall within the category of international law governing the use of force, and therefore should be dealt with using the tenets provided by that branch of law. The main assertion of this essay is that ethical and legal issues surrounding some Active Cyber Defense measures can effectively be handled through the legal framework provided by the Caroline formulation of the preemptive doctrine.