An anonymous reader shares a report: China's widening crackdown on bitcoin trading resulted in a travel ban of sorts for two executives from the country's largest commercial bitcoin exchanges, which regulators are closing down. From a report: On Thursday, top executives of two Chinese digital currency exchanges who were scheduled to speak at an industry conference in Hong Kong didn't show up and their sessions were canceled. The event's organizer, a bitcoin-trading firm called Bitkan, didn't provide a reason. The two executives were Lin Li, chief executive of Huobi, and Justin Pan, who the event organizer listed as being the chief operating officer of OKCoin. The two-day conference was originally supposed to be held in Beijing but its organizers last week decided to shift the venue to Hong Kong after Chinese regulators earlier this month ordered digital-currency exchanges to wind down their operations. Software pioneer and former fugitive John McAfee -- a high-profile but controversial character in the bitcoin industry -- told conference attendees on Wednesday that top executives from the major bitcoin exchanges are currently not allowed to leave China.