David P. Fidler, visiting professor of law
Whether biological agents are “means of warfare” or only “methods of warfare” based on direct or indirect effects has not been a major policy or legal question. Smallpox and other pathogens that cause adverse biological and societal cascades are considered “repugnant to the conscience of mankind” because of the totality of their direct and indirect effects. The indirect effects of pathogenic infection are proximate to the direct action of the pathogen on the host and sufficiently severe in the human body and the body politic to take into account.
This treatment of biological agents perhaps suggests that deciding whether cyber capabilities constitute a means of warfare should involve consideration of the nature and scale of indirect effects and not just the direct effects of code on target computer systems. The indirect effects of malware can be proximate to the direct impact of the code and, potentially, severe enough within the target system and beyond to warrant inclusion in the determination of a means of warfare.
Read the full piece in the Council on Foreign Relations.