The Winklevoss twins, Cameron and Tyler, best known for their legal battle with Facebook's (NASDAQ:FB) Mark Zuckerberg, filed an initial public offer, or IPO, request with the U.S. Securities and Exchange Commission, on Monday, to float an exchange-traded fund, which will allow investors to trade in bitcoins -- a form of digital currency.

The proposal filed by the New York-based Winklevoss Bitcoin Trust, if approved, will allow any investor to trade in bitcoin shares, by creating an exchange-traded fund, or ETF, which will track the digital currency as if it were a commodity like gold or silver.

According to the filing, the Trust will initially sell $20 million worth of bitcoin shares, which “represent units of fractional undivided beneficial interest in and ownership of the Trust.” The filing also says that the offer is aimed at investors "seeking a cost-effective and convenient means to gain exposure to Bitcoins with minimal credit risk."

Bitcoins were first introduced as a crypto-currency in 2009 by an anonymous group of developers under the pseudonym 'Satoshi Nakamoto.' The currency operates on a peer-to-peer electronic cash system and is not managed by any central agency or banking regulator. Bitcoins are used as an online alternative to cash in many parts of the world.

Bitcoins are produced by a process called bitcoin mining, in which the miner has to solve complex algorithms to create new bitcoins. Currently, there are about 11 million bitcoins in the system and new coins will be created through a tightly controlled process until the total number of coins in circulation reaches 20 million, which is expected to happen by the year 2140.

Bitcoins, touted as a currency of the future by its promoters, is gaining acceptance worldwide as an alternative to holding cash. However, its critics dismiss the currency as a temporary fad, pointing to the lack of regulatory control over it.

Last month, U.S. Federal Reserve officials said they are investigating possible risks for online payment systems such as PayPal Inc. and Bitcoin, as bankers worry that new online players could disrupt the financial system and online currency could be abused for money-laundering schemes.

Bitcoin's opponents also have expressed their concerns over high volatility in the value of bitcoins in the past year. The value of a single bitcoin rose to more than $266 in April, from $13 in January, before retreating to its current value of about $100.

Bitcoins are traded through online networks and the process of acquiring and selling them involves complex procedures limiting its exposure to those with a certain amount of technological know-how. 

The Winklevoss brothers revealed last month that they held bitcoins worth $11 million -- 1 percent of the total bitcoins available at the time -- according to a New York Times report.