| Several States, including Austria, Estonia, France, Germany, Japan, the Netherlands, the United Kingdom, and the United States, have expressly confirmed the applicability of the law of countermeasures to cyber operations. Others, including Brazil, China, and Cuba, have expressed caution in this regard. Countermeasures should be distinguished from retorsions, which are unfriendly but lawful acts by the aggrieved party against the wrongdoer.
As a matter of general international law, an injured State may only take countermeasures against the responsible State if the following conditions are met:
Additionally, the countermeasures must fulfil the following requirements:
Taken countermeasures must be suspended if the internationally wrongful act has ceased and if “the dispute is pending before a court or tribunal which has the authority to make decisions binding on the parties”, and they must be terminated as soon as the responsible State has complied with its (secondary) obligations.
There is a debate as to whether States that have not themselves been directly injured by an unlawful cyber operation may engage in countermeasures in support of the injured State (sometimes referred to as collective countermeasures). In particular, one State has recently put forward the view that non-injured States “may apply countermeasures to support the state directly affected by the malicious cyber operation”. This would apply where diplomatic action is insufficient, but no lawful recourse to use of force exists. This interpretation would allow States to offer active assistance to States, which may not possess sufficient cyber capabilities themselves to counter an ongoing unlawful cyber operation. This view has found some support in scholarship, but was since rejected by at least one other State, with other parts of scholarship reluctant to endorse it. Therefore, it has to be regarded as a call for progressive development of international law, rather than a statement of the current state of international law.
Whether a particular measure fulfils these conditions is an objective question, while the burden of proof that the relevant conditions have been fulfilled falls on the injured State. The exact standard of proof required is unsettled in international law and it will depend on the relevant forum. However, relevant international jurisprudence tends to rely in this regard on the standard of “clear and convincing evidence”. This standard translates in practice into a duty to “convince the arbiter in question that it is substantially more likely than not that the factual claims that have been made are true.” Importantly, if a State does resort to countermeasures on the basis of an unfounded assessment that a breach has occurred, it may incur responsibility for its own wrongful conduct.
"If a State is the victim of an internationally wrongful cyber operation and another State can be held responsible under customary international law on State responsibility, the injured State may, depending on the circumstances, be entitled to take countermeasures.
A countermeasure is an act that would otherwise be contrary to international law, but where the injured State can invoke the prior internationally wrongful act as a ground for precluding wrongfulness. If there is doubt regarding the attribution of a cyber operation to a State under international law, it may be preferable for the injured State to make use of acts of retorsion rather than countermeasures in order to avoid the possibility of incurring State responsibility for its response.
Countermeasures may only be taken to induce a State to cease an internationally wrongful act or resume its compliance with an international obligation. They are not to be used for punishment and retaliation. Countermeasures must be limited to what is considered necessary and proportional, and may only target the State to which the cyber operation or internationally wrongful act can be attributed. There is no requirement for countermeasures to be of the same nature as the internationally wrongful acts to which they are a response, and countermeasures in response to cyber operations may therefore be carried out within or outside cyberspace. Countermeasures must not violate the prohibition on the threat or use of force or international humanitarian law.
The State held responsible should be notified of both the violation of international law and the grounds for attribution, as well as of the intention to introduce countermeasures. Countermeasures may only be taken if a State has sufficient grounds for attributing the conduct in question to a particular State under international law. What constitutes sufficient grounds will be fact-specific and case-specific, and can be particularly challenging to determine in the case of cyber operations. The State taking countermeasures must be confident in its attribution before resorting to countermeasures. However, the State taking countermeasures need not publish detailed grounds for its attribution or give a detailed technical account of this to the State identified as responsible as this might reveal sensitive methods of interception and detection or offensive and defensive capabilities.
Countermeasures may be taken without prior notification to the responsible State if providing such notification might reveal sensitive methods or capabilities or prevent the countermeasures from having the necessary effect. For example, the injured State could carry out a cyber operation to disrupt the capability of the aggressor State conducting the internationally wrongful cyber operation such as election interference. This countermeasure would in other circumstances be in violation of the aggressor State’s sovereignty."
"Even if malicious cyber activity against a State has not risen to the level of an armed attack entitling the victim State to exercise the right of self-defence, international law provides that a victim State that is subjected to another State’s internationally wrongful act against it (whether through malicious cyber activity, or physical means) is entitled to have recourse to counter-measures which are consistent with international law.
Malicious cyber activity attributable to a State that interferes with a victim State’s proper governing functions is an example of an internationally wrongful act."
"Consistent with the de-escalatory nature of international law, there are clear restrictions on the actions that a victim state can take under the doctrine of countermeasures. A countermeasure can only be taken in response to a prior internationally wrongful act committed by a state, and must only be directed towards that state. This means that the victim state must be confident in its attribution of that act to a hostile state before it takes action in response. In cyberspace of course, attribution presents particular challenges, to which I will come in a few moments. Countermeasures cannot involve the use of force, and they must be both necessary and proportionate to the purpose of inducing the hostile state to comply with its obligations under international law.
These restrictions under the doctrine of countermeasures are generally accepted across the international law community. The one area where the UK departs from the excellent work of the International Law Commission on this issue is where the UK is responding to covert cyber intrusion with countermeasures.
In such circumstances, we would not agree that we are always legally obliged to give prior notification to the hostile state before taking countermeasures against it. The covertness and secrecy of the countermeasures must of course be considered necessary and proportionate to the original illegality, but we say it could not be right for international law to require a countermeasure to expose highly sensitive capabilities in defending the country in the cyber arena, as in any other arena.
In addition, it is also worth stating that, as a matter of law, there is no requirement in the doctrine of countermeasures for a response to be symmetrical to the underlying unlawful act. What matters is necessity and proportionality, which means that the UK could respond to a cyber intrusion through non-cyber means, and vice versa."
"Resort may be had to countermeasures in response to an internationally wrongful act, in accordance with international law, in relation to States’ activities in cyberspace as in relation to their other activities. This includes both resorting to countermeasures against a State whose cyber activities constitute internationally wrongful acts and carrying out countermeasures by means of cyber operations. Countermeasures need not be symmetrical: where the internationally wrongful act is itself not a cyber activity, the response may nonetheless involve cyber-based countermeasures (and vice versa).
An injured State may only take countermeasures against a State which is responsible for an internationally wrongful act in order to induce that State to comply with its obligations. Any measures adopted must be commensurate with the injury suffered. They must be carried out in accordance with the conditions and restrictions established in international law and must in particular not contravene the prohibition on the threat or use of force, must be necessary and proportionate to the purpose of inducing the responsible State to comply with its obligations and must not contravene any other peremptory norm of international law.
The application of international law to the use of countermeasures in cyberspace must take account of the nature of cyber activities, which might commence and then cease almost instantaneously or within a short timeframe. In those circumstances, a wider pattern of cyber activities might collectively constitute an internationally wrongful act justifying a response.
The UK does not consider that States taking countermeasures are legally obliged to give prior notice (including by calling on the State responsible for the internationally wrongful act to comply with international law) in all circumstances. Prior notice may not be a legal obligation when responding to covert cyber intrusion with countermeasures or when resort is had to countermeasures which themselves depend on covert cyber capabilities. In such cases, prior notice could expose highly sensitive capabilities and prejudice the very effectiveness of the countermeasures in question. However any decision to resort to countermeasures without prior notice must be necessary and proportionate to the purpose of inducing compliance in the circumstances."
"The customary international law doctrine of countermeasures permits a State that is the victim of an internationally wrongful act of another State to take otherwise unlawful measures against the responsible State in order to cause that State to comply with its international obligations, for example, the obligation to cease its internationally wrongful act. Therefore, as a threshold matter, the availability of countermeasures to address malicious cyber activity requires a prior internationally wrongful act that is attributable to another State. As with all countermeasures, this puts the responding State in the position of potentially being held responsible for violating international law if it turns out that there wasn’t actually an internationally wrongful act that triggered the right to take countermeasures, or if the responding State made an inaccurate attribution determination. That is one reason why countermeasures should not be engaged in lightly.
Additionally, under the law of countermeasures, measures undertaken in response to an internationally wrongful act performed in or through cyberspace that is attributable to a State must be directed only at the State responsible for the wrongful act and must meet the principles of necessity and proportionality, including the requirements that a countermeasure must be designed to cause the State to comply with its international obligations—for example, the obligation to cease its internationally wrongful act — and must cease as soon as the offending State begins complying with the obligations in question.
The doctrine of countermeasures also generally requires the injured State to call upon the responsible State to comply with its international obligations before a countermeasure may be taken—in other words, the doctrine generally requires what I will call a “prior demand.” The sufficiency of a prior demand should be evaluated on a case-by-case basis in light of the particular circumstances of the situation at hand and the purpose of the requirement, which is to give the responsible State notice of the injured State’s claim and an opportunity to respond.
I also should note that countermeasures taken in response to internationally wrongful cyber activities attributable to a State generally may take the form of cyber-based countermeasures or non-cyber-based countermeasures. That is a decision typically within the discretion of the responding State and will depend on the circumstances."
"Depending on the circumstances, DoD lawyers may also consider whether an operation that does not constitute a use of force could be conducted as a countermeasure. In general, countermeasures are available in response to an internationally wrongful act attributed to a State. In the traditional view, the use of countermeasures must be preceded by notice to the offending State, though we note that there are varying State views on whether notice would be necessary in all cases in the cyber context because of secrecy or urgency. In a particular case it may be unclear whether a particular malicious cyber activity violates international law. And, in other circumstances, it may not be apparent that the act is internationally wrongful and attributable to a State within the timeframe in which the DoD must respond to mitigate the threat. In these circumstances, which we believe are common, countermeasures would not be available."
- Scenario 04: A State’s failure to assist an international organization
- Scenario 05: State investigates and responds to cyber operations against private actors in its territory
- Scenario 06: Cyber countermeasures against an enabling State
- Scenario 09: Economic cyber espionage
- Scenario 14: Ransomware campaign
- Scenario 17: Collective responses to cyber operations
Notes and references
- ILC Articles on State Responsibility, Commentary, part 3 ch 2 at para 1.
- Austria, Pre-Draft Report of the OEWG - ICT: Comments by Austria (31 March 2020), stating that ‘a violation of the principle of State sovereignty constitutes an internationally wrongful act – if attributable to a State – for which a target State may seek reparation under the law of State responsibility. A target State may also react through proportionate countermeasures.’ (emphasis added).
- Estonia, ‘President of the Republic at the opening of CyCon 2019’ (29 May 2019), stating that “states have the right to react to malicious cyber operations, including using diplomatic response but also countermeasures”
- French Ministry of the Armies, ‘International Law Applied to Operations in Cyberspace’ (9 September 2019) 6, stating that ‘In response to a cyberattack, France may consider diplomatic responses to certain incidents, countermeasures, or even coercive action by the armed forces if an attack constitutes armed aggression.’
- Germany, ‘Statement by Ambassador Dr Thomas Fitschen, Director for the United Nations, Cyber Foreign Policy and Counter-Terrorism, Federal Foreign Office of Germany’ (November 2018) 3, stating that ‘in case of a cyber operation that is in breach of an international legal obligation below the level of the use or threat of force prohibited by Art. 2 (IV) [of the UN Charter] States are also entitled to take countermeasures as allowed by international law.’
- Japan, ‘Japan’s Position Paper for the Report of the United Nations Open-Ended Working Group on “Developments in the Field of Information and Telecommunications in the Context of International Security”’ (undated), stating that ‘Japan recognizes that basic rules on State responsibility including those on countermeasures applies to cyberspace.’
- Dutch Ministry of Foreign Affairs, ‘Letter to the parliament on the international legal order in cyberspace’ (5 July 2019) 7.
- United Kingdom, ‘Statement on Other Disarmament Measures and International Security to the 72nd UNGA First Committee’ (23 October 2017), stating that ‘We reaffirm that the law of state responsibility applies to cyber operations in peacetime, including the availability of the doctrine of countermeasures in response to internationally wrongful acts.’
- Brian J. Egan, ‘Remarks on International Law and Stability in Cyberspace’ (10 November 2016), stating that countermeasures are available ‘to address malicious cyber activity’ if that activity amounts to a prior internationally wrongful act attributable to another State.
- Brazil, ‘Open-ended Working Group on developments in the field of information and telecommunications in the context of international security: Second Substantive Session - New York, 11 February 2020: Statement by the Delegation of Brazil’ (11 February 2020), stating that ‘In the case of malicious acts in cyberspace, it is often difficult to attribute responsibility to a particular State or actor with unqualified certainty. A decision to resort to countermeasures in response to such acts carries a high risk of targeting innocent actors, and of triggering escalation.’
- China, ‘Statement by the Chinese Delegation at the Thematic Debate of the First Committee of the 72th UNGA’ (October 2017), stating that ‘Countries should discuss application of international law in the manner conducive to maintain peace, avoid introducing force, deterrence and countermeasures into cyberspace, so as to prevent arms race in cyberspace and reduce risks of confrontation and conflicts.’
- Cuba, ‘Declaration by Miguel Rodríguez, Representative of Cuba, at the Final Session of Group of Governmental Experts on Developments in the Field of Information and Telecommunications in the Context of International Security’ (23 June 2017), registering ‘serious concern over the pretension of some, reflected in para 34 of the draft final report, to convert cyberspace into a theater of military operations and to legitimize, in that context, unilateral punitive force actions, including the application of sanctions and even military action by States claiming to be victims of illicit uses of ICTs.’ (emphasis added).
- ILC Articles on State Responsibility, Art 49 para 1; Case Concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia) (Judgment) 1997 ICJ Rep 7, para 83.
- ILC Articles on State Responsibility, Art 52 paras 3 - 4.
- ILC Articles on State Responsibility, Art 52 para 1 subpara a). According to the UK Attorney General, the UK does not feel legally obliged, when taking countermeasures in response to a covert cyber intrusion, to “give prior notification to the hostile state”. UK Attorney General, Jeremy Wright QC MP, ‘Cyber and International Law in the 21st Century’.
- ILC Articles on State Responsibility, Art 28-41; the list of consequences includes (i) continued duty of performance, (ii) cessation and non-repetition, (iii) reparation, and (iv) particular consequences of a serious breach of obligations under peremptory norms of general international law.
- ILC Articles on State Responsibility, Art 52 para 1 subpara b) – Art 52 para 2.
- ILC Articles on State Responsibility, Art 49(1); Case Concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia) (Judgment) 1997 ICJ Rep 7, para 87. The list of consequences in Art 28-41 includes (i) continued duty of performance, (ii) cessation and non-repetition, (iii) reparation, and (iv) particular consequences of a serious breach of obligations under peremptory norms of general international law.
- ILC Articles on State Responsibility, Art 49(3).
- Such as the obligation to refrain from the threat or use of force as embodied in the UN Charter, obligations for the protection of fundamental human rights, and obligations of a humanitarian character prohibiting reprisals. ILC Articles on State Responsibility, Art 50(1).
- ILC Articles on State Responsibility, Art 50(2).
- Articles on State Responsibility, Art 51; Case Concerning the Gabčíkovo-Nagymaros Project (Hungary/Slovakia) (Judgment) 1997 ICJ Rep 7, para 85.
- ILC Articles on State Responsibility, Art 54.
- President of Estonia, Kersti Kaljulaid, ‘President of the Republic at the opening of CyCon 2019’ (29.05.2019).
- Michael N Schmitt, ‘Estonia Speaks Out on Key Rules for Cyberspace’ Just Security (10.06.2019), considering the Estonian interpretation to be “an advantageous development in the catalogue of response options that international law provides to deal with unlawful acts”.
- French Ministry of the Armies, International Law Applied to Operations in Cyberspace, p. 10, arguing that collective countermeasures are not authorised under international law.
- Jeff Kosseff, ‘Collective Countermeasures in Cyberspace,’ (2020) Notre Dame Journal of International & Comparative Law Vol. 10, Iss. 1, 34; François Delerue, Cyber Operations and International Law (CUP 2020), 457.
- ILC Articles on State Responsibility, Commentary in Part 3, Chapter 2 on Art 49, para 3.
- ILC Articles on State Responsibility, Commentary to Part One, Chapter 5, para 8 (noting that “[i]n a bilateral dispute over State responsibility, the onus of establishing responsibility lies in principle on the claimant State”).
- See, eg, Trail Smelter case (United States v Canada) (Award) 1941 3 RIAA 1905, 1965; see also Robin Geiss and Henning Lahmann, ‘Freedom and Security in Cyberspace: Shifting the Focus Away from Military Responses Towards Non-Forcible Countermeasures and Collective Threat-Prevention’ in Katharina Ziolkowski (ed), Peacetime Regime for State Activities in Cyberspace (NATO CCD COE 2013) 624 (noting that in cases where State responsibility is involved, the required threshold tends to shift towards ‘clear and convincing’”).
- James Green, ‘Fluctuating Evidentiary Standards for Self-Defence in the International Court of Justice’ (2009) 58 ICLQ 163, 167 (emphasis original).
- ILC Articles on State Responsibility, Commentary in Part 3, Chapter 2 on Art 49 para 3.
- Official compendium of voluntary national contributions on the subject of how international law applies to the use of information and communications technologies by States, UNODA, A/76/136, August 2021, 72-73.
- Official compendium of voluntary national contributions on the subject of how international law applies to the use of information and communications technologies by States, UNODA, A/76/136, August 2021, 84.
- Attorney General Jeremy Wright:Cyber and International Law in the 21st Century, 23 May 2018
- United Kingdom Foreign, Commonwealth & Development Office, Application of international law to states’ conduct in cyberspace: UK statement, 3 June 2021
- Brian J. Egan, International Law and Stability in Cyberspace, 10 November 2016 21-22.
- Hon. Paul C. Ney, Jr., DOD General Counsel Remarks at U.S. Cyber Command Legal Conference, 2 March, 2020