When a state suffers an internationally wrongful act at the hands of another state, international law allows the injured state to respond in a variety of ways. Depending on the nature, scope, and severity of the initial wrongful act, lawful responses can range from a demand for reparations in response to a low-level violation to a forcible act of self-defense in response to an armed attack. Countermeasures offer an additional way for a state to respond to an internationally wrongful act. Countermeasures are acts that would in general be considered internationally wrongful but are justified to address the wrongdoing state’s original international law violation. As states increasingly employ cyber tools to commit hostile acts against their adversaries, countermeasures are poised to play a growing role in interstate relations. This chapter explores the role that countermeasures can play in the US cyber strategy known as Defend Forward.
Ashley S. Deeks, Defend Forward and Cyber Countermeasures, in The United States’ Defend Forward Cyber Strategy: A Comprehensive Legal Assessment, Oxford University Press, 181–203 (2022).