Yesterday it was the US Treasury's Financial Crimes Enforcement Network that tightened its grip on businesses that accept Bitcoin. Today, it is China, where the world's largest Bitcoin exchange by trading volume, BTCChina announced that he had received word from "above" that his platform would no longer be able to accept renminbi from BTC buyers. "As of right now, we have received notice from our third-party payment company that they will disallow customers from making deposits into our exchange," Bobby Lee, a former Yahoo developer who co-founded BTCChina this year, told the Financial Times. The result, not surprisingly, is an overnight crash in BTC, which crashed by 50% from $900 two days ago to just $455 hours ago.

More from the FT:

With its booming market for commerce, China had been seen by Bitcoin enthusiasts as fertile ground for the virtual currency. However, regulators were concerned that people could use Bitcoins to skirt the country’s capital controls. They also grew alarmed at the rampant speculative demand for Bitcoins, warning it had the makings of a bubble. The Chinese central bank took a hard line two weeks ago, banning the country’s financial institutions from handling Bitcoin transactions. Although the People’s Bank of China said individuals were still free to trade it at their own risk, the ban on third-party payment service providers from doing Bitcoin business effectively makes new purchases of the virtual currency impossible. “I’m not that surprised,” said Hong Hao, chief China strategist at Bank of Communications. “Even if the amount of Bitcoin in circulation wasn’t that large yet, it was a potential threat to the monetary system.” Mr Lee of BTCChina said the emphasis of the notice was on deposits, meaning that customers with existing renminbi balances would still be able to withdraw their cash from the exchange. “They are completely safe,” he said, adding that people with money already deposited on the exchange still had the option of buying Bitcoins. ... China’s capital controls mean it takes time for investors to arbitrage the difference between prices in and outside the country.

In a world where the central banks are actively engaged in gold capital controls (and have been for over 40 years), and the BIS has its own in-house gold prices suppression team, nobody could have possibly seen this coming.

We are, of course, joking. But some who apparently were angry and did not see this coming, were the computer hackers of the world. As @george_chen reports, the PBOC reported it was promptly DDOSed in retaliation for China's overnight crackdown on Bitcoin.

BREAKING NEWS: CHINA CENTRAL BANK (PBOC) WEB UNDER ATTACK; UNSTABLE FOR ACCESS; LOCAL MEDIA BLAME BITCOIN INVESTORS pic.twitter.com/uXEoPWfxoP — George Chen (@george_chen) December 18, 2013