The Winklevoss twins, Cameron and Tyler, who became famous after their public legal battle with Mark Zuckerberg over Facebook, have invested heavily in bitcoins, a digital currency that has recently become almost as valuable as gold.

According to a profile in the New York Times, they own close to one percent of all bitcoins on the market, worth about $11 million. The Winklevoss have slowly accrued their collection of bitcoins since last summer, when they were worth about $20. As of Thursday, they are worth around $120, with the entire market worth about $1.3 billion.

Bitcoins and their owners are difficult to locate, as part of their appeal was the general anonymity associated with the currency. The twins are the first public figures to openly disclose their investment in the bitcoin market.

Bitcoin trading happens online, where transactions are handled on a peer-to-peer network where bitcoin miners, who operate the servers, approve each transaction, with the value being determined by users. They are also not regulated by a bank.

Many fear that the digital currency could be used for money laundering or other illegal activities before it becomes an accepted form of currency with legitimate digital retailers. The U.S. Department of Treasury most recently said virtual currencies such as bitcoins need to begin establishing more rules to curb criminal activity.

The New York Times has equated the bitcoin popularity to "tulip mania" when Dutch tulip bulbs reached astronomically high prices in 1637 before collapsing, as bitcoins reached all-time highs on Wednesday of $266. 

"To say highly speculative would be the understatement of the century," said Steve Hanke, a professor at Johns Hopkins University and expert in alternative currencies, speaking about bitcoins.

In addition to the Winklevoss twins, venture capitalists and hedge fund companies are looking to find a fortune with the virtual currency, and Cameron Winklevoss says he understands the skepticism.

"At some point that narrative will shift to 'virtual currencies are here to stay.' We're in the early days," Winklevoss said.

Market experts say that as quickly as the bitcoin has risen to prominence, it has fallen, but that it is too early to predict whether bitcoins will continue to lose value. There could be a point where they settle into a stable range instead of the fluctuations that have occurred over the last three days.