Might be useful to add (maybe in a footnote) the recent statement by the United Kingdom re the notice requirement for countermeasures.
"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."
Full text available here: https://www.gov.uk/government/speeches/cyber-and-international-law-in-the-21st-century