This article highlights legal problems of cyber attacks from a ‘jus ad bellum’ perspective (international dispositions regarding the justification for entering a war). Since no international instrument whatsoever cover the cyber attacks the analogies with current international solutions are largely employed. We illustrate also the developments with relevant examples taken from main powers’ doctrine and practice (US, Russia and China). The starting points are the provisions regarding the use of (armed)"force" under Article 2(4) and “armed attack” under Article 51 of United Nations Charter. The qualification of a cyber attack as use of “armed force” or “armed attack” is based a multi criteria threshold developed by Schmitt. Other developments focus the capacity of present International law concepts (direct and indirect armed attack, identification of the aggressor state, pertinence of pre-emptive or interceptive self defense vis-à-vis cyber ‘armed attack’, etc.) to answer cyber warfare’s structures and challenges.