Bitcoin tumbled as much as 20% Tuesday. The price of the volatile digital currency dipped below $12,000, its lowest level in more than a month, according to data from CoinDesk.com. Other popular cryptocurrencies ethereum and ripple also posted double-digit losses. It's unclear why bitcoin fell. Cryptocurrency is a murky market with frequent swings. "Volatility is quite common in the cryptocurrency world," said Mati Greenspan, a Tel Aviv-based analyst at investment firm eToro. The plunge follows a Bloomberg report on Monday that Chinese officials were stepping-up measures to limit cryptocurrency trading, which is ... (full story)