Back in October, we marveled that a then-unknown company named BTC-China had suddenly become the world's most popular Bitcoin exchange, helping to push the value of the digital currency over $200.

But less than three months later, Bitcoin prices have quadrupled, and there's a new top dog in China: another virtually unknown company called Huobi.

At the moment, Bitcoin is the Wild West of international finance – an international peer-to-peer network of computers that, as a whole, lies out of the reach of any one country's regulation. But when Bitcoin bumps against closely regulated financial services businesses, things become even wilder. That's what's happening in China, where regulators stepped in last month to forbid financial services companies from doing business with the Bitcoin exchanges – a move that instantly changed the landscape.

Big Chinese businesses that were warming up to Bitcoin, such as search giant Baidu, suddenly dropped it. Bitcoin prices plunged.

It appeared that the government was going to make it tricky, if not impossible, to fund Bitcoin exchange accounts. But that hasn't turned out to be the case. Big companies like Alibaba have dropped bitcoin business, but the exchanges are still doing business, they've just been forced to make a few changes. "In the past month, things have been quite interesting here in terms of Bitcoin," says Bobby Lee, the CEO of BTC China.

While the Central Bank guidelines made things more difficult for Bitcoin businesses, they did not outlaw the currency altogether. And that was enough for people like Lee. "Because Bitcoin exchanges have been given legal room to exist, they essentially found different ways to accept money for deposit," he says.

Since customers can no longer use payment processors to fund accounts, BTC-China has hacked together a voucher system that let's new people set up accounts without actually transferring money to the Chinese exchange. Instead, customers who want to cash out are selling their BTC-China dollars as vouchers on sites such as Paipai.com, an online retail site similar to eBay. To fund a BTC-China account, they simply enter their voucher code on the exchange's website. "There's a healthy network of resellers who are selling vouchers," says Lee.

Meanwhile, China's two other big exchanges – Huobi and OKCoin – are bypassing payment processors by letting users wire money directly into exchange bank accounts, says Scott Freeman, a China-based entrepreneur who is also a Bitcoin investor. That's a slower process, but he says that since the December regulatory changes, trading has gone on in the country pretty much unabated. Lee says that BTC-China isn't going the direct payment route because they would first need to be licensed as a payment processor to receive and pay out money from BTC-China's corporate bank account.

Huobi's big advantage seems to boil down to one thing: it does not charge trade commissions, while its competitors do. Apparently, nothing beats a free product when you're an upstart company looking to gain market share. And as Reddit readers have pointed out, a commission-free exchange is an attractive crash pad for automated trading software, which seeks to profit on Bitcoin's daily ups and downs.

According to Lee, BTC-China dropped its trading fees in September, right before the fall run-up in Chinese Bitcoin trading. But when China's regulators stepped in in December, Lee decided to reinstate them in order to disarm criticism that the trading freebies were contributing to a speculative Bitcoin bubble. OKCoin followed suit, but not Huobi.

With its trading fees and voucher system BTC-China has seen its role as the top Chinese Bitcoin exchange slip. According to BTCKan.com, a market data aggregator, the exchange now ranks third in China when measuring the volume of trades. In an email interview, Huobi CEO Leon Li said his exchange has stolen market share from competitors because it offers "better service, user experience and promotion."

How long Huobi will be able to stay on top, however, is unclear. "China's a tough market," Freeman says.