4.In certain circumstances actions in cyberspace may constitute a violation of the prohibition of the use of force The prohibition on the threat or use of force is laid down in Article 2(4) of the Charter of the United Nations’? and customary international law. According to the Advisory Opinion of the International Court of Justice on the legality of the threat or use of nuclear weapons?3, an action may be considered the use of force irrespective of the means used. What matters are the effects of the actions taken. As a result, it cannot be ruled out that in some circumstances a cyberattack will reach such a threshold that it will be deemed the use of force. Perceiving a cyberattack as the use of force is supported by the possibility of it causing similar effects to those caused by a classic armed attack executed with the use of conventional weapons. When assessing whether or not acyber operation reaches the threshold of the use of force, the situation must be analysed individually, taking into consideration the circumstances of actions taken in accordance with the requirements of international law. An action in cyberspace that leads to: a permanent and significant damage of a power plant, a missile defence system deactivation or taking control over an aircraft or a passenger ship and causing an accident with significant effects may be considered the use of force. This list is not exhaustive — the legal qualification will always depend on the circumstances of a specific attack. A cyberattack that does not reach the threshold of the prohibited use of force may be deemed a prohibited intervention or an action that violates the principle of sovereignty. 5. Acyberattack may be qualified as an armed attack. The right to self-defence applies to cyberspace Pursuant to Article 51 of the Charter of the United Nations and customary international law, a state has the right of self-defence in the event of an armed attack. In the context of cyberspace, a cyberattack that results in death or injury of people or damage or destruction of property of significant value may be considered an armed attack. In such circumstances, according to international law, a state enjoys the right of self-defence, however, this right should be exercised in line with the principles arising from namely the principle of necessity and proportionality.*4 customary international law, Self-defence does not need to involve the same means through which the armed attack was inflicted. In response to a cyberattack that reaches the threshold of an armed attack, it is possible to respond both in cyberspace exclusively or with the use of traditional armed forces. Deprivation of the right to respond to such a cyberattack with kinetic means could render the self-defence right illusory when the perpetrator of an armed attack is little dependent on its functioning in cyberspace. 12 Article 2(4) of the Charter of the United Nations: “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.” 13 Advisory Opinion of the International Court of Justice on the Legality of the Threat or Use of Nuclear Weapons, ICJ Rep. 1996, § 39. 14 Advisory Opinion of the International Court of Justice on the Legality of the Threat or Use of Nuclear Weapons, ICJ Rep. 1996, § 41.