The bitcoin mining rush is sputtering. Speculators, known as miners, use powerful computers to solve complex software problems and verify transactions to unlock new bitcoins. They’re finding that the enterprise isn’t as profitable as it once was. Drawn by the virtual currency’s jump in value last year, digital prospectors have turned the mining industry into an arms race as they buy expensive computing equipment and gobble up electricity. While that worked well as long as bitcoin’s value kept rising, smaller players are now being crowded out by bigger competition, high utility bills and declining prices. “If you mine ... (full story)