On Wednesday 30th January 2013 Professor Dan Saxon, Visiting Professor at the University of Leiden spoke at an event held by the Hughes Hall Hat Club. This talk was the second of a three-part series, exploring the legal challenges for armed forces resulting from the development and use of new military technologies for the conduct of warfare. This lecture asks how will international law, in particular international humanitarian law ("IHL"), govern cyber warfare? Military experts, academics, lawyers and policy makers are just beginning to address this complex question. During armed conflict, should "cyber attacks" be subject to the same legal restrictions as more traditional, kinetic armed attacks? If so, how will soldiers who attack the enemy and defend themselves during cyber warfare distinguish between combatants and civilians? Do cyber weapons render the idea of "proportionate attacks" meaningless since computer viruses and other tools have the potential to harm countless computer networks and other infrastructure? What precautions must planners of cyber attacks implement to minimise damage to civilian objects. This lecture describes the challenges of applying the basic principles of IHL to the "armed conflicts" that are fought, more and more, with computers.