The world is gearing up for cyberwar. The US Cyber Command became operational in November. Nato has enshrined cyber security among its new strategic priorities. The head of Britain’s armed forces said recently that boosting cyber capability is now a huge priority for the UK. And we know China is already engaged in broad cyber espionage attacks against the west. So how can we control a burgeoning cyber arms race? We may already have seen early versions of cyberwars in Estonia and Georgia, possibly perpetrated by Russia. It’s hard to know for certain, not only because such attacks are often impossible to trace, but because we have no clear definitions of what a cyberwar actually is. Do the 2007 attacks against Estonia, traced to a young Russian man living in Tallinn and no one else, count? What about a virus from an unknown origin, possibly targeted at an Iranian nuclear complex? Or espionage from within China, but not specifically directed by its government? To such questions one must add even more basic issues, like when a cyberwar is understood to have begun, and how it ends.