453 denmark’s position paper As the ICJ Stated in the Corfu Channel Case7, States are under an “obligation not to knowingly allow its territory to be used for acts contrary to the right of other States”. This obligation is a natural corollary of a State’s sovereignty over persons and cyber infrastructure on its territory. As a general rule due diligence requires States to take all reasonable measures to prevent, eliminate and mitigate potentially significant harm to legally protected interests of another State, or the international community as a whole. The general principle of due diligence has developed with some variation in different fields of international law, including international environmental law, transboundary harm, and human rights. Similarly, Denmark believes that the precise contours of the due diligence obligation in cyberspace will continue to develop and crystalize in the coming years. It is, however, possible to set out some key features. Due diligence is an obligation of conduct, not of result. A State is obliged to take all reasonable measures to stop or prevent a given cyber act from occurring. Not all harmful cyber operations emanating from another State’s territory entail due diligence obligations and corresponding rights of the target State. While there is still scope for State practice to clarify the precise threshold, Denmark subscribes to the view that the harm suffered must be significant and not merely amount to inconveniences or minor disruptions. The lack of compliance with a State’s due diligence obligations may lead another State to take countermeasures if the conditions set out below in section 7 are fulfilled. 7 Countermeasures States may be subject to unfriendly or hostile cyber acts or omissions that do not rise to the level of illegality under international law. These may be met with responses of a diplomatic, economic, or political nature intended to deter and hold accountable such States, irrespective of the fact that those acts are not illegal under international law. Such responses are generally termed retorsions. However, where one State breaches its obligations under international law towards another State, the victim State may respond with countermeasures. A State injured by an internationally wrongful act may be justified in taking non-forcible countermeasures in order to procure the cessation of the wrongful act and to achieve reparation for the injury. 7 United Kingdom of Great Britain and Northern Ireland v. Albania (merits), p. 22. Downloaded from Brill.com 03/27/2024 10:42:51AM distributed under the terms of the CC BY 4.0 license. https://creativecommons.org/licenses/by/4.0/ via Open Access. This is an open access article Nordic Journal of International Law 92 (2023) 446–455