Could you invent an autonomous hacking system that could find and fix vulnerabilities in computer systems before criminals could exploit them, and without any human being involved? That's the challenge faced by seven teams competing in Darpa's Cyber Grand Challenge in August. Each of the teams has already won 750,000 for qualifying and must now put their hacking systems up against six others in a game of "capture the flag". The software must be able to attack the other team's vulnerabilities as well as find and fix weaknesses in their own software – all while protecting its performance and functionality. The winning team will walk away with 2m.