This publication 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, the book also addresses cyberespionage and political activism in cyberspace. Starting by providing an overview of the technical background, the author explains the vulnerabilities of critical infrastructure. Then he outlines notable cyberincidents that have occured so far and analyzes pertinent state practice and policies. Turning to the legal analysis, the primary focus is 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 applicable to cyberspace, in particular in the light of an evident civilization 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. Finally, juridictional pitfalls borne in cyberspace are looked into. The final chapter is dedicated to providing recommendations to the international community, in order to address cyberthreats in a political process.