CYIL vol. 12 (2021)

martina Šmuclerová CYIL 12 (2021) “WannaCry” cyberattack on British hospitals in May 2017, or “NotPetya” malware attack hitting hospitals in Virginia and Pennsylvania in June 2017 directly threatened the lives of people, and caused fatality in the first case. The above conclusions apply to self-defence in response to a cyberattack regardless of whether it uses conventional or digital tools. Since an extensive, generally accepted reinterpretationof Art. 51with respect topreemption is not probable and a formal revision of the UN Charter not realistically conceivable, 38 in view of Article 108, it is appropriate to investigate the domain of an international custom. III. Preemptive self-defence in cyberspace as an international custom If the UN Charter or any other international conventional norm does not provide for the right to a preemptive self-defence, and in cyberspace in particular, the proponents of such a rule may turn to the customary field. Does an international customary norm of preemptive self-defence applicable to cyberspace exist? What are the prerequisites of this norm? Does the State practice confirm such a custom? First, it is necessary to remind the two constitutive elements of an international custom as confirmed by the ICJ, namely the uniform, constant and general practice and the legal conviction of States that such a practice is corroborated by an international legal norm ( opinio iuris sive necessitatis ) 39 , and to assess the States’ conduct in this light. Since the potential of the creation of a new exception to Art. 2 (4) is at stake, in other words further negation of an act of aggression which is at the heart of the provision, an aggravated level of restrictions applies: in light of the ius cogens threshold, an acceptance and recognition of such conduct as lawful by the international community of States as a whole (Art. 53 of Convention of Vienna on the Law of Treaties ) would be required. 1. International custom of self-defence similar to Article 51 The existence of a customary norm of self-defence, parallel to Art. 51, was already assessed by the ICJ in the Nicaragua Case, as mentioned above. Both the conventional and customary norm co-exist in harmony and the core prerequisite – the existence of an armed attack – is identic to both. Other elements of the legal regime of self-defence arise either from the UN Charter (UN Security Council’s authority) or the customary domain (principle of necessity and proportionality). The Court explains in this regard: “[T]he Charter, having itself recognized the existence of this right, does not go on to regulate directly all aspects of its content. For example, it does not contain any specific rule whereby self-defence would warrant only measures which are proportional to the armed attack and necessary to respond to it, a rule well established in customary international law. Moreover, a definition of the ‘armed attack’ which, if found to exist, authorizes the exercise of the ‘inherent right’ of self-defence, is not provided in the Charter, and is not part of treaty law. It cannot therefore be held that Article 51 is a provision which ‘subsumes and 38 For such a proposal, see Cassese, A., Article 51. In: Cot, J.-P., Pellet, A., Forteau, M., La Charte des Nations Unies: Commentaire article par article , 3e éd. 2005, Paris, pp. 1342–1343. 39 Continental Shelf (Libyan Arab Jamahiriya/Malta) , judgment of 3 June 1985, ICJ Reports 1985 , § 27; Nuclear Weapons , op. cit. note 29, p. 253; Asylum Case (Colombia v. Peru) , judgment of 20 November 1950, ICJ Reports 1950 , p. 277; North Sea Continental Shelf Cases (Federal Republic of Germany v. Denmark; Federal Republic of Germany v. Netherlands) , 20 February 1969, ICJ Reports 1969 , p. 43.


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