Does the advent of cyber war require us to abandon the traditional ethical framework for thinking about the morality of warfare – just war theory – and develop principles specific to the unique nature of cyber attacks? Or can just war theory still provide an appropriate basis for thinking through the ethical issues raised by cyber weapons? This article explores these questions via the issue of whether a cyber attack can constitute a casus belli. The first half of the article critically engages with recent attempts to provide a new theory of just information warfare (JIW) that is supposedly better suited to the unique character of cyber war insofar as it is grounded the broader meta-ethical framework of information ethics (IE). Yet the article argues that not only is JIW fundamentally unsuitable as a way of thinking about cyber war, but (in the second half) that it is possible to develop a different account of how we can understand a cyber attack as constituting a casus belli in a way that is in keeping with traditional just war theory. In short, there is no need to reinvent just war theory for the digital age.