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Silicon Valley is ramping up its real money bets on the virtual money Bitcoin.

Andreessen Horowitz, a leading venture capital firm, announced on Thursday that it had led a $25 million fund-raising round for Coinbase, a Bitcoin start-up in San Francisco that aims to help virtual currencies gain mainstream acceptance.

Chris Dixon, a partner at Andreessen Horowitz who will join Coinbase’s board, said on Thursday that “it’s hard to overstate the excitement of a certain segment of the technology community.”

“Every day somebody comes in and says, ‘Bitcoin is going to be as big as the Internet,’ “ Mr. Dixon said.

The size of the Coinbase investment dwarfs the previous largest fund-raising effort by a Bitcoin company. Circle Internet Financial, a start-up that processes digital money payments for merchants, raised $9 million in October from investment firms including Accel Partners.

While Bitcoin has many naysayers who have called it a speculative bubble and a playing field for frauds, a growing number of mainstream players say it has the potential to be a sort of Internet for money, smoothing the electronic movement of cash. Last week, Bank of America released the first significant research note on digital money, laying out its potential. But the biggest excitement has been among technology insiders like Mr. Dixon.

“We aren’t thinking that Amazon is going to be using Bitcoin tomorrow, but I think they will be in five years,” Mr. Dixon said. “It’s one of the five best computer science ideas of the last 40 years.”

A steady stream of Silicon Valley investors has been building stakes in virtual currency start-ups. Last month, a Chinese Bitcoin exchange raised $5 million from Lightspeed Venture Partners. Google’s venture capital arm has put money into a couple of companies in the space, Buttercoin and Ripple Labs. Coinbase has also attracted money from Union Square Ventures and Ribbit Capital.

Bitcoin, created by anonymous programmers in 2009, is a digital currency produced by a network of users competing against one another to solve computer problems, a method known as “mining.” The open-source program that created it determined that only 21 million coins would ever be created, leading to a speculative boom that pushed the price of one Bitcoin to more than $1,000 recently from around $200 at the start of November.

The growth has led to uncertainty about how regulators will deal with digital money. Chinese authorities last week barred financial institutions in the country from participating in virtual currency transactions. American regulators, on the other hand, have made cautiously supportive statements about the trend.

Silicon Valley investors generally hope that Bitcoin will move past the current stage and settle into a more stable period that will allow it to be used as a system for making payments and sending money around the world.

Since its founding a little more than a year ago, Coinbase has developed a reputation as one of the most reliable players in the often chaotic world of virtual currencies.

The company enables merchants to accept digital money for ordinary purchases and allows customers to trade Bitcoins and hold them in online wallets. Coinbase says it is adding 10,000 online wallets daily and now hosts 600,000 wallets, up from 200,000 just a few months ago.

Coinbase said it planned to use the new money to expand its staff and “promote the mainstream adoption of Bitcoin.”

The company added that the world was “nearing a tipping point for broad adoption of Bitcoin — what we at Coinbase believe to be one of the most important shifts in the global economy in our lifetime.”

Virtual currencies are accepted at a growing number of merchants. The company Bitpay said this week that it had processed more than $100 million in transactions this year. But this is tiny compared with the number of transactions made by speculators and people buying illicit goods.

Mr. Dixon said that Bitcoin had been too complicated for most people who are not technology specialists. But he said that services like Coinbase made it easier to access, opening it to broader use. Some merchants hope that virtual currencies will let them avoid the 2 to 3 percent that they pay on every credit card transaction.

In another step in Bitcoin’s expansion, the leading nonprofit advocacy group for digital money, the Bitcoin Foundation, said on Thursday that it was opening a London office and creating a program for international affiliates that will include the Bitcoin Association of Australia and the Bitcoin Foundation Canada. The Bitcoin Foundation’s primary operations are based in Washington.