Virtual currencies have become a haven for black market entrepreneurs, for libertarians in love with privacy and, apparently, for those with a penchant for financial fraud. The federal government puts Homero Joshua Garza in the final group.

A digital entrepreneur, Garza launched a computer repair company while still in high school. By age 21, he was running two tech companies with more than 20 employees. Last year, still not yet 30, Garza was being described by a national publication as a “cryptocurrency tycoon” who had launched his own competitor to Bitcoins — a virtual currency called Paycoin.