Bitcoin sheds Mt.Gox albatross, rallies nearly 20 percent

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Is bitcoin bulletproof?

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In spite of being hit on all sides by bad news, the embattled virtual currency rallied sharply on Monday by nearly 20 percent, as questions swirled around the demise of the world's largest bitcoin exchange.

As regulators and prosecutors encircled Mt.Gox, the bitcoin trader that sought bankruptcy protection last week with nearly $500 million of virtual currency vanishing into the ether, bitcoin extended its rally.

(Read more: How to make money from bitcoin)

The cryptocurrency plunged immediately after the disclosure of Mt.Gox's troubles, but began a quiet surge late last week as the world's attention shifted elsewhere. Some analysts think the worst news may already be discounted in bitcoin's price, and that investors could be separating bitcoin and the defunct exchange.

A user scans a QR code on a smartphone, transferring bitcoins into their digital wallet.
David Ryder | Getty Images

"There's a lot of really good news coming out that's not getting attention," said Austin Alexander, deputy director of The Bitcoin Center in New York. He pointed to several positive developments, including a ruling by British authorities that bitcoin would receive the same tax treatment as other foreign currencies, as providing a boost to the virtual currency's spot price.

He speculated that investors may also be searching for safe havens as Ukraine's confrontation with Russia reaches a boiling point, and engulfs world powers in a standoff.

"It just doesn't bode well for the world economic picture," Alexander said, adding that big venture capitalists like Marc Andreessen were still bullish on the currency.

According to The Wall Street Journal, Mt.Gox is the target of an investigation by the U.S. attorney's office. Prosecutors have subpoenaed the company, a person familiar with the matter told the newspaper.

(Read more: Back to work at bitcoin's embattled Mt.Gox)

Although the currency has true believers, billionaire investor Warren Buffett isn't among them. In a "Squawk Box" interview Monday, the Oracle of Omaha told CNBC that bitcoin "isn't a currency" and that he wouldn't be surprised to see its complete demise in 10 to 20 years.

(Read more: Warren Buffett: Ukraine won't stop my stock-buying)

Bitcoin was trading under $700 on Monday afternoon, a gain of about 18 percent on the day, according to CoinDesk.

—By CNBC's Javier E. David