This chapter questions the direct applicability of the just war tradition’s principle of distinction to electronic attacks involving computer network exploitation (CNE). It offers three principle challenges to maintaining the norm of distinction in electronic attacks that are rooted in the impossibility of foreknowledge of the object of attack in a computer network. In lay terms, without significant inside assistance it is impossible for a hostile agent seeking to exploit a computer network from knowing the network’s architecture and role prior to conducting hostile exploitation of the network. Due to this lack of knowledge, it is impossible for the hostile agent to be certain that initial exploitation will be free of negative consequences. This draws attention to the understanding of hostile action in both CNE and computer network attacks (CNA). This impossibility of foreknowledge leads to three challenges in applying the principle of distinction to cyber attacks: the access problem – where if CNE is considered to be an attack, then our understanding of distinction collapses, the boundary problem – where it may be impossible for an agent to know the boundaries or couplings of the system that they are attacking, and the levels problem – where humans are held accountable for non-human agency inherent in the deployment of autonomous software programmes (‘viruses’, ‘malware’, etc). This chapter argues that these problems are surmountable, but not with an understanding of distinction that is directly transposed from human interactions.