Logo: to the web site of the Swedish Defence University

The concept of hybrid attacks has entrenched itself in the discourse on security matters. However, oneissue on which there has been little to no discussion is the question of how to make hybrid attacks costfor the attacker. One possibility that has been mentioned is to use force in response to hybrid attacks.To explore this issue further, the purpose of the thesis was to find out if a state is allowed to use forcein response to a hybrid attack by another state. Hence, the research question was ‘does internationallaw allow states to unilaterally use force in response to a hybrid attack by another state?’ To help findan answer to the research question, three subsidiary questions were asked: 1) What is the threshold forthe use of force? 2) What is the definition of hybrid attacks? 3) How do hybrid attacks relate to use offorce?

The thesis was divided into five chapters. The first was an introduction, the second dealt with the firstsubsidiary question (the Threshold of the use of force), the third dealt with the second and third sub-sidiary question (definition of hybrid attacks, and the relation between hybrid attacks and the use offorce), the fourth chapter was a discussion from which the answer to the research question emanated,and the fifth chapter was a reflection on the findings of the thesis.

The answer to the research question was that international law does allow states to unilaterally use force inresponse to a hybrid attack by another state. The reason that this is case is two folded: First, the Thresholdof the use of force (when states are allowed to use force unilaterally) is equated with the availability ofself-defence. The availability of self-defence demands that the principles of necessity and proportion-ality are satisfied in the given situation. Second, given that measures of hybrid attacks can be classifiedas use of force, they can potentially pass the Threshold of the use of force, which in turns means thatthe use of force is a potential response to hybrid attacks.