The Fortress Investment Group reported a paper loss of $3.7 million from investments in Bitcoin, the first large public company to disclose a stake in the volatile virtual currency.

Fortress said it bought $20 million worth of Bitcoin in 2013, according to a filing with the Securities and Exchange Commission on Thursday.

As of Dec. 31, that stake was worth less than $17 million.

Related Links Mt. Gox Files for Bankruptcy

Executives at Fortress have expressed interest in Bitcoin for months, but it has been unclear just how the company might be involved with it.

Ripple Labs, a budding online Bitcoin payment system, had disclosed an investment from Pantera Capital, which includes money from executives at Fortress.

The Fortress filing on Thursday did not detail the exact nature of its virtual currency investment, and a spokesman for Fortress declined to comment.

Bitcoin, which exists only as computer code, has thus far circumvented the traditional financial system. That has posed a challenge for regulators, which now face increased pressure in the wake of the collapse of Mt. Gox, one of the earliest and at one point largest Bitcoin exchanges.

Fortress’s investment in Bitcoin represents a tiny fraction, less than 1 percent, of a balance sheet valued at $2.6 billion at the end of 2013. But its stake could encourage interest in an industry that has not yet gained a foothold with Wall Street or the general economy.

“This makes it more legitimate for the hedge funds to buy, and easier, and provide the path for any other public company to report it,” said Gil Luria, a managing director at Wedbush Securities. “Now, there’s a blueprint for how to go through reporting ownership of Bitcoin in a public S.E.C. filing.”

Banks have largely shied away from Bitcoin because of its volatility and lack of regulation. That has fueled Bitcoin’s instability, and the price has fluctuated wildly since the currency was introduced in 2009.

But venture capital firms and other established entrepreneurs have begun to back new Bitcoin companies with more sophisticated infrastructure and technology. That’s fueled some hopes that Bitcoin could gain more of a foothold in the mainstream.

“I think the question now is whether they’re going to market this as a product to their investors,” Mr. Luria said of Fortress’s investment. “I think that would be the next step I would expect from them.”