Although such operations are a very old and common practice, it is paradoxically not regulated by a single and coherent legal regime under international law.
Only the status of spies in times of war is, in fact, subject to specific international rules.
The development of new technologies and communication media has, likewise, heightened possibilities for mass surveillance.
In June 2013, the revelations made by Edward Snowden, a former agent of the National Secret Agency (NSA), concerning the United States’ intelligence programs reinvigorated legal and political debate around espionage activities by states.
The third view holds that espionage stands in a grey area of international law, as it is neither explicitly forbidden nor clearly authorized.
Yoo and Sulmasy 2007 argues that this is because states do not have an interest in regulating espionage, as doing so would hinder their capacity to protect their national security.
In response, Forcese 2016 warns against the perverse side effects that such approaches could have on the overall international legal system.
Russell Buchan is senior docent in internationaal recht aan de universiteit van Sheffield in Groot-Brittannië en is van 19 augustus tot en met 13 september als Visiting Fellow verbonden aan het The Hague Program for Cyber Norms van het Institute of Security and Global Affairs van de Universiteit Leiden.
In face of these uncertainties, some authors have thus sought to establish abstract models for evaluation.
Deeks 2016 thus advocates for a “pragmatic” system that would determine the legality of acts of espionage depending on the interests at stake.