Cyberwar (military operations conducted via computer networks) is often downplayed compared to traditional military operations as they are largely invisible to outside observers, difficult to convincingly attribute to a particular source and rarely cause physical damage or obvious harm. We use mediation theory to argue that cyberwar operations cause harm by undermining trust in computerised devices and networks and by disrupting the transparency of our usage of information technology in our daily lives. Cyberwar operations militarise and weaponise the civilian space of the Internet by co-opting and targeting civilian infrastructure and property. These operations (and the possibility of such operations occurring) fundamentally change users’ Internet experience by fostering fear and paranoia about otherwise unnoticed and transparent aspects of their lives, similarly to how biological and chemical weapons create fear and paranoia about breathing, eating, and physical exposure to the world. We argue that the phenomenological aspects of cyberwar operations offer a compelling justification for prohibiting cyberwar in the same manner in which biological and chemical warfare are prohibited.