In 2007 Estonia was faced with a new type of international violence that was difficult to conceptualise. Characterisations of the cyber attacks by Estonian officials at the time ranged from war, crime to terrorism. The technological makeup of cyberspace led to a range of problems for the traditional distinctions between these categories and hence international law was uncertain in its application to this new form of violence. These issues are among those generally discussed in literature on cyber attacks and international law. This literature also tends to follow a typical pattern of writing about law and technology, and arguably this does not result in a developed understanding of the relationship between law and technology. However, another body of literature exists which seeks to understand the intersection of law and technology better by looking at past events where technology created problems for the law, the socio-technical context of the law and the values that law seeks to protect. By adopting the insights from this body of literature, the uncertainties that cyber attacks (technology) creates for law will be explored. Accordingly, it will be shown that cyber attacks create a number of uncertainties for international law. On one level, this new type of violence has created uncertainties in the application of existing law and thus led to legal issues. These are centred around doctrinal issues on state responsibility (particularly attribution) and what constitutes an illegitimate use of force. On another level, they raise uncertainties about the compatibility of law premised upon a technological environment in which state sovereignty is central to regulate behaviour in an environment in which states lack a monopoly of violence and distinctions between the actors inflicting this violence is less clear. Exploring these uncertainties will lead to a more developed appreciation of how technology can shape the way we understand violence in international law.