Ashley Deeks is the E. James Kelly, Jr.–Class of 1965 Research Professor at the University of Virginia Law School. She serves on the State Department’s Advisory Committee on International Law and the Board of Editors for the American Journal of International Law. She is a senior fellow at the Miller Center and a senior contributor to Lawfare.
Understanding when and how states may lawfully deploy countermeasures is critical for states operating in the cyber arena—not only to understand their own options when injured but also to anticipate the responses that their cyber activities may trigger from other states. This essay examines the role that countermeasures may play in the US cyber strategy of Defend Forward and argues that some states are developing a lex specialis of cyber countermeasures.