Mike Caldwell, the founder of a small company in Salt Lake City that makes timekeeping software, considers himself financially conservative. He’s also a geek, and couldn’t help but get excited late last year when he heard about bitcoin, a new virtual currency. In February, on one of the handful of online exchanges that have appeared over the past year, he bought about $20,000 worth at less than a dollar per bitcoin. “I felt that maybe I would get a 20 or 50 percent return,” says Caldwell, 33. By early June, when he sold the last of his stake, a bitcoin was worth around $30. Caldwell says his total return was well over 1,000 percent. “That magnitude was totally unexpected,” he says.