This chapter analyses the main circumstances in which a cyber operation may constitute an internationally wrongful act. The first observation made, which is developed in the first section, is that there is no general prohibition of cyber operations in international law. Cyber operations between States are not per se prohibited by international law and generally constitute unfriendly or hostile acts. Despite the absence of a general prohibition on cyber operations, the carrying out of a cyber operation may lead to a violation of specific norms of international law. This chapter focuses on the primary norms of international law that can be breached by state-sponsored cyber operations, namely State sovereignty, non-intervention and human rights.