It reads like a morality tale for the information age: a lone inventor dreams up a clever new way to do business online – until a big, bad e-commerce giant comes along to steal his invention and make millions from it.

This kind of digital David and Goliath tale has become a cliché of US patent law. Small patent owner sues giant technology company: it happens every day. But unlike in fairy tales, the morality of these lawsuits is not always clear. Sometimes the little guy is really the troll – and he is just using a bunch of otherwise worthless patents to extort a price from the e-commerce giant who wants to cross his bridge.