Cyber operations represent one of the main security threats today. The number of cyber operations attacking critical infrastructure is increasing year by year and states are looking for means to defend against this threat. However, the origin of hostile cyber operations is often located in the territory of another state, and attacked states must therefore grapple with the question of international law in their search for an effective defence mechanism. If states wish to defend themselves actively, the sovereignty of another state may be infringed, and such an infringement must be justified by an instrument of international law. These instruments of international law are retorsion, countermeasures, self-defence and plea of necessity. Application of plea of necessity, unlike the other alternatives mentioned, is not premised on the attributability of the cyber operation to the state, and it is precisely the attribution of cyber operation that poses one of the main problems of taking legal defensive measures. The article is divided into two parts. The first part is devoted to the relationship between retorsion, countermeasures, self-defence and plea of necessity. The second part discusses the conditions for the application of plea of necessity in the cyber context. The text takes into account the available state practice, in particular the national positions on the application of plea of necessity in the cyber context published in the last three years.

Summary The article is devoted to the issue of the use of force in self-defense against cyber operations aimed at financial and banking infrastructure that cause only economic (non-material) damage. The article deals with the relationship between the described type of cyber operation and economic coercion, presenting the conclusion that these are different acts, which are subject to a different regime of international law regulation. Attention is also paid to the analytical approaches that can be used to bring cyber operations under the regime of the regulation of the use of force. The main contribution of the article is to capture the evolution of the scholarly debate and state practice in relation to non-destructive cyber operations in the period after the publication of Tallinn Manual 2.0 (post-2017), concluding that even non-destructive cyber operations (including cyber operations against critical financial infrastructure) can fulfil the characteristics of both use of force and armed attack, based on newly available sources, in particular official national positions on the application of international law in cyberspace published by states.