We discuss robotic weapons, their advantages and disadvantages, and their effect on the way humans wage war. We consider the factors favoring the development of lethal robotic weapons that can operate autonomously. We discuss the attempt to mitigate the dangers inherent in such weapons by means of an ethical controller implemented in software. We conclude that this is impossible to achieve and therefore that autonomous lethal robotic weapons should not be developed.Workshop: III Ethicomp latinoaméricaRed de Universidades con Carreras en Informática (RedUNCI