The book revolves around the public international law aspects of the destructive use of cyberspace by state actors and non-state actors, encompassing cyberwar, cyberterrorism, and hacktivism, but excluding cybercrime. For the purpose of delimitation, it also addresses cyberespionage and political activism in cyberspace. By providing an overview of the technical background, the book explains the vulnerabilities of critical infrastructure. It outlines notable cyberincidents occurred so far and analyzes pertinent state practice and policies. Turning to the legal analysis, it primarily focuses on the contemporary jus ad bellum and jus in bello, exploring whether concepts like the use of force or self-defense, are applicable to cyberattacks, despite their lack of physicality, or whether state responsibility and the principles of International Humanitarian Law are applicaple to cyberspace, in particular in the light of an evident civilianization of battlespace in this area. Furthermore, the book encompasses destructive cyberterrorism and opposes it to the use of cyberspace for terrorist purposes, and puts this into context with human rights aspects of political activism in cyberspace. It also looks into jurisdictional pitfalls borne in cyberspace. After a brief summary of the research results, the final chapter is dedicated to providing recommendations to the international community, in order to address cyberthreats in a political process.