CYIL vol. 12 (2021)

martina Šmuclerová CYIL 12 (2021) States which become direct victim of an imminent cyberattack or main cyberpowers with a high degree of probability to become a target (or even the aggressor?) are to adhere to such a stand. Secundo , does a public announcement or stipulation of such right in a national strategy or piece of legislation amount to a precedent launching the process of emergence of a new custom, or the very action must be effectively taken? Is the reaction by other States to the pioneer stands announced by France, US, UK, and Australia cardinal at this moment? In other words, does the absence of condemnation or criticism amount to an acquiescence of such precedents opening the door to the emergence of a new custom? For the moment, no State has expressly criticized the position of the proponents of the preemptive self-defence in reaction to a cyberattack. On the other hand, States that have publicly claimed their right to self-defence in cyberspace have conditioned it by the occurrence of a cyberattack, as shown above. In all cases, it is already at this level of potential formation of a custom that the position of States is cardinal. As Max Planck Encyclopedia notes “[the] practice consists in what the subjects of international law do and say, both of which can be mere facts—or be perceived so—or evidence of opinio iuris”. 55 Manifestations of practice as regards what States say include, in particular, “government statements in the domestic framework ( eg declarations in parliament) or in an international framework (notes or declaration[s] setting out protest[s] or claims, reactions to other States’ claims, statements and documents submitted in international organizations and conferences)”. 56 As regards “ what States do , one may mention material behaviours such as movements of troops, economic and other measures taken as countermeasures or retaliation, movements of fleets or aircraft.” 57 The States’ public announcements, including their claims of the right to preemptive self-defence in cyberspace, thus constitute an important element of the material component of a custom. Notably the positions of States with respect to draft proposals of international legal instruments, including soft law declarations or guidelines at international fora, such as the OEWG, “have in recent times become particularly important because they may contribute to the formation of precise and detailed customary international rules [… T]hey can directly influence the attitude of other States or cause reactions on their part” 58 . It is therefore essential that States take active part in the ongoing discussions in the framework of the United Nations OEWG and GGE and other international platforms dedicated to international law and ICT since their stand contributes to the crystallization of an international custom. Indications of widespread opinio iuris might diminish or even disappear the need for corresponding behaviour. Acquiescence or passivity of States constitutes itself a legal fact impacting on the emergence of an international custom of preemptive self-defence in cyberspace. Tertio , it is expectable that a State resorting to preemptive self-defence might not publicize such act, in line with strategic urgencies and the already existing hesitation to publicly disclose the information about attribution of the hostile cyber activity 59 – does it impact on 55 Treves, T., Customary International Law, November 2006. In: Max Planck Encyclopedia , op. cit. note 23, para. 10. 56 Ibid ., para. 26 (emphasis added). 57 Ibid ., para. 27 (emphasis added). 58 Ibid ., para. 27 (emphasis added). 59 France, for example, stresses its sovereign right not to publicly announce the attribution to a particular State

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