The laws of armed conflict (LOAC), based on norms, conventions, and treaty law, attempts to demarcate bright lines of separation between permissible uses of deception, such as a ruse, and impermissible, or treacherous, uses of deception, such as perfidy. While some types of deception are unproblematic from a legal perspective, others are not. This chapter examines the legal and moral permissibility of deceptive cyberoperations. It argues that if we hold fast to the internationally legally recognized and customary rule prohibiting perfidy, then any use of a cyberweapon that results in the killing, wounding, or capture of an adversary is impermissible and amounts to perfidy. Given this conclusion, the chapter suggests that the long-term effects of cyberoperations may undermine or erode the minimal trust necessary between belligerents. In particular, the (over)reliance on cyberoperations may threaten the ability to negotiate peaceful settlements and adversely affect international stability.