The race to create a successful virtual currency
Bitcoin has caught the imagination of digital gold miners throughout the world. It may be the cleverest virtual currency yet, with anonymous roots that give it a creation myth like something out of the Da Vinci Code. Other e-currencies have tried and failed, usually by losing credibility with users or hitting legal problems with governments. Here are six that failed to create the money to make the digital world go round, and three still trying to gain currency.