23/06/2024
The U.S. Department of Defense’s Dictionary of Military Terms defi nes “computer network
attack” (CNA) as “[a]ctions taken through the use of computer networks to disrupt, deny,
degrade, or destroy information resident in computers and computer networks, or the computers
and networks themselves.”1 NATO adopts this defi nition in its Glossary of Terms, but adds the
parenthetical that “[a] computer network attack is a type of cyber attack.”2 Curiously, it does not
defi ne “cyber attack” and the reference contains the sole mention of “cyber” in the document.
The term “computer network attack” is adequately descriptive for non-legal use. For instance,
it usefully distinguishes such operations from computer network defence, computer network
Michael N. Schmitt
International Law Department
United States Naval War College
Newport, U.S.A.
[email protected]
2012 4th International Conference on Cyber Confl ict
C. Czosseck, R. Ottis, K. Ziolkowski (Eds.)
2012 © NATO CCD COE Publications, Tallinn
Permission to make digital or hard copies of this publication for internal use within
NATO and for personal or educational use when for non-profi t or non-commercial
purposes is granted providing that copies bear this notice and a full citation on the
first page. Any other reproduction or transmission requires prior written permission
by NATO CCD COE.
1 U.S. Department of Defense, Dictionary of Military and Associated Terms, Joint Publication 1-02, Nov. 8,
2010, as amended through Feb. 15, 2012, available at http://www.dtic.mil/doctrine/dod_dictionary/. 2 NATO Standardization Agency, NATO Glossary of Terms and Defi nitions (AAP-6) (2010), at 2-C-12.
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exploitation and other cyber activities.3 Despite practical utility, its use causes measurable
disquiet among lawyers, for “attack” is a legal term of art that has specifi c meaning in the
context of two very different bodies of international law governing State behaviour in times of
crisis or confl ict. In both cases, the term represents a consequential threshold that delineates the
legality of particular cyber operations, and, in some cases, the lawfulness of responses thereto.
This article seeks to bridge the terminological gap between the legal and non-legal communities
by examining and explaining the signifi cance of the word “attack” in international law.
Hopefully, doing so will imbue policy makers, cyber operators and technical experts with
greater sensitivity to the legal dimensions of the verbiage they employ when addressing cyber
matters. Although the two communities may not speak the same language, members of both
benefi t from being bilingual.
2. THE LEGAL ARCHITECTURE
The international law governing confl ict consists of two distinct bodies of law: the jus ad
bellum and the jus in bello. Jus ad bellum norms govern when States, as an instrument of their
national policy, may resort to force. They address, inter alia, the prohibition of the use of force
by States and the exceptions thereto, most notably the right of self-defence and authorization or
mandate by the UN Security Council.4 The jus in bello, by contrast, deals with how the military
and other armed actors may employ force, including who and what may be targeted.
These norms, also labelled the “law of armed confl ict” or “international humanitarian law”
(the latter term adopted in this article), apply in situations of “armed confl ict” irrespective
of whether the State or armed actor in question has resorted to force in compliance with the
jus ad bellum. Differing objects and purposes animate the two bodies of law and explain the
impenetrable barrier between them. The jus ad bellum seeks to maintain peaceful relations
within the community of nations by setting strict criteria as to when States may move beyond
non-forceful measures such as diplomacy, economic sanctions and counter-measures.5 Of
particular note is the right to do so in self-defence when either facing an “armed attack” or
coming to the aid of another State which is defending itself (collective self-defence). By
3 Computer network operations comprise “computer network attack, computer network defense, and related
computer network exploitation enabling operations. DoD Dictionary of Military Terms, supra note 1.
Computer network defense is defi ned as “[a]ctions taken to protect, monitor, analyze, detect and respond
to unauthorized activity within Department of Defense information systems and computer networks,”
whereas computer network exploitation encompasses “[e]nabling operations and intelligence collection
capabilities conducted through the use of computer networks to gather data from target or adversary automated information systems or networks.” Id. 4 U.N. Charter, arts. 2(4), 42 & 51.
5 Countermeasures are “measures that would otherwise be contrary to the international obligations of
an injured State vis-à-vis the responsible State, if they were not taken by the former in response to an
internationally wrongful act by the latter in order to procure cessation and reparation.” Draft Articles on
Responsibility of States for Internationally Wrongful Acts, Report of the International Law Commission on the Work of its 53rd sess., UNGAOR, 56th sess., sup. No. 10 (A/56/10), ch. IV.E.1, at p. 128,
available athttp://untreaty.un.org/ilc/texts/instruments/english/commentaries/9_6_2001.pdf [hereinafter
Articles of State Responsibility]. Note that Article 50 of the Articles of State Responsibility provides that
countermeasures cannot amount to a use of force. However, this position, which the author accepts, was
challenged by Judge Simma in the Oil Platforms case, where he argued that countermeasures could involve
force when in response to an act that itself amounted to a use of force, but did not qualify as an armed attack. Oil Platforms (Islamic Republic of Iran v. U.S.), 2003 I.C.J. 161, ¶¶12-13 (Nov. 6) (separate opinion
of Judge Simma).
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contrast, international humanitarian law seeks to minimize harm during an armed confl ict that
is either unnecessary to effectively accomplish legitimate military aims or excessive relative
to them. It does so most directly by establishing legal boundaries for the conduct of “attacks.”
Ignoring “right or wrong” under the jus ad bellum optimizes this purpose.
Since the term “attack” applies in separate bodies of law with discrete objects and purposes, it
is unsurprising that its meaning differs depending on its source. In the jus ad bellum, it appears
in Article 51 of the United Nations Charter: “Nothing in the present Charter shall impair the
inherent right of individual or collective self-defence if an armed attack occurs against a
Member of the United Nations, until the Security Council has taken measures necessary to
maintain international peace and security.” Article 51, recognized as refl ective of customary
international law by the vast majority of legal scholars, is an express exception to Article 2(4)
of the Charter, which provides that “[a]ll 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.” Taking the
Articles together, a State may “use force” without violating Article 2(4) when it is the victim
of an “armed attack”, as that term is envisaged in Article 51. Self-defence requires no ex ante
authorization from the Security Council, States alone enjoy the right of self-defence, and the
right only attaches to armed attacks with a transnational element.6
In international humanitarian law, “attack” refers to a particular category of military operations.
Article 49(1) of the 1977 Additional Protocol I to the 1949 Geneva Conventions defi nes
“attacks” as “acts of violence against the adversary, whether in offence or in defence.”7 It is a
neutral term in the sense that some attacks are lawful, whereas others are not, either because of
the status of the object of the attack or how the attack is conducted. Neutral though it may be,
“attack” is operatively a key threshold concept in international humanitarian law because many
of its core prohibitions and restrictions apply only to acts qualifying as such.
It is important to bear in mind that this notion only attains relevance once an “armed confl ict”
is underway. Like “attack”, “armed confl ict” is a legal term of art referring to two types of
confl icts: 1) international armed confl icts, which are between States; and 2) non-international
armed confl icts, which are confl icts at a certain level of intensity and organization between a
State and an organized armed group or between organized armed groups.8 Absent a situation
qualifying as one of these confl icts, domestic and human rights law, not humanitarian law,
governs the activities in question.
6 In the cyber context, the meaning of the term “use of force” is highly unsettled. See Manual on the International Law Applicable to Cyber Warfare (Tallinn Manual), (Michael N. Schmitt et al. eds., Cambridge
University Press, forthcoming 2013) [hereinafter Tallinn Manual].
7 Protocol Additional to the Geneva Conventions of 12 August 1949, and Relating to the Protection of
Victims of International Armed Confl icts, art. 49.1, June 8, 1977, 1125 U.N.T.S. 3 [hereinafter AP I].
8 For the thresholds applicable to international and non-international armed confl ict, see common articles 2
and 3 respectively to the four Geneva Conventions. Note that in addition to situations involving hostilities,
the applicability of humanitarian law extends to those in which there has been a declaration of war or occupation, even when hostilities have not broken out. Convention for the Amelioration of the Condition of the
Wounded and Sick in Armed Forces in the Field, Aug. 12, 1949, 6 U.S.T. 3114, 75 U.N.T.S. 31; Convention for the Amelioration of the Condition of Wounded, Sick and Shipwrecked Members of Armed Forces
at Sea, Aug. 12, 1949, 6 U.S.T. 3217, 75 U.N.T.S. 85; Convention Relative to the Treatment of Prisoners
of War, Aug. 12, 1949, 6 U.S.T. 3316, 75 U.N.T.S. 135; Convention Relative to the Protection of Civilian
Persons in Time of War, Aug. 12, 1949, 6 U.S.T. 3516, 75 U.N.T.S. 287.
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To summarize, an “armed attack” is an action that gives States the right to a response rising
to the level of a “use of force,” as that term is understood in the jus ad bellum. By contrast,
the term “attack” refers to a particular type of military operation during an armed confl ict to
which particular international humanitarian law norms apply. T
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