In the 1970s and 1980s, a generous spirit suffused the Internet, whose users were few and far between. But today, the net is ubiquitous, connecting billions of people, machines and essential pieces of infrastructure -- leaving us vulnerable to cyber-attack or meltdown. Internet pioneer Danny Hillis argues that the Internet wasn't designed for this kind of scale, and sounds a clarion call for us to develop a Plan B: a parallel system to fall back on if -- or when -- the Internet crashes.