A state’s right to self-defense depends on whether an attack on the state is regarded an act of war according to jus ad bellum. The UN Charter does not specifically mention cyber warfare and it is therefore unclear whether a cyber-attack can be classified as an act that corresponds to an armed attack. The debate amongst scholars has not led to consensus on the meaning of the concept of cyber warfare nor whether it can be regarded as an act of war. The purpose of this study was to analyze the concept of cyber warfare according to the theory of good concepts formed by John Gerring. The study aims to answer the questions of whether the definitions meet Gerring's criteria for a good concept and if any of the analyzed definitions can be considered compatible with jus ad bellum and thus give a state the right to self-defense. This study uses a qualitative concept analysis and analyzes three different definitions of cyber warfare with a focus on intention, effect and actor respectively. The results show that all definitions meet all the criteria to some extent. The actor-focused definition was considered a good concept at a high level, the intention-focused definition at a low level and the effect-focused at a very low level. Only Hathaway's effect-focused definition could in itself be considered compatible with jus ad bellum. The other definitions would require a more comprehensive interpretation of the UN Charter.