A new kind of computer con has emerged in the past few years. It's technically mundane but psychologically brutal: using false threats of arrest, scammers trick low-income victims into repaying debts that do not exist. And one rainy day last January, they accidentally targeted one of the smartest hackers around. Mike Davis is a good guy who gets to play at being a bad guy, a man who gets paid handsomely for testing the limits of his clients' security systems. Davis wanted a new challenge; when the fraudsters called, he realised he'd found it.