A bitcoin mining company in Slovenia has been hacked, for the possible theft of tens of million of dollars, renewing questions about the security of the virtual currency just days before it is due to start trading on major U.S. exchanges.

The Wall Street Journal reports the hack attack totalled $70 million.

The news could take some steam out of the momentum that has driving the value of the cryptocurrency to record levels.

The virtual currency leaped above $13,000 for the first time Wednesday – only hours after it hit $12,000. It topped $14,000 on Thursday morning then surged past $17,000 as the frenzy surrounding the virtual currency escalated just days before it starts trading on major U.S. exchanges. Bitcoin has gained more than $5,000 in just the past two days.

At the same time, there are fresh concerns about the security of bitcoin and other virtual currencies after NiceHash, a company that mines bitcoins on behalf of customers, said it is investigating a breach that may have resulted in the theft of about $70 million worth of bitcoin.

Research company Coindesk said that a wallet address referred to by NiceHash users indicates that about 4,700 bitcoins had been stolen. NiceHash said it will stop operating for 24 hours while it verifies how many bitcoins were taken. Wallet is a nickname for an online account.

As of 11:15 a.m. EST, bitcoin was valued at $17,482, according to Coinbase, the largest bitcoin exchange. At the start of the year, one bitcoin was worth less than $1,000.

Bitcoin has crashed through a series of milestones in recent weeks despite warnings of a potential bubble. After starting the year below $1,000, it hit $8,000 for the first time in early November and topped $11,000 just last week.

Much of the stunning ascent has been driven by the expectation that big, professional investors are set to start trading it. It’s also been propelled by mom-and-pop investors who don’t want to miss its meteoric rise.

CNN provides an update on the rapid rise in a video report.

Temporary shutdown

NiceHash said it is investigating a security breach and will stop operating for 24 hours while it verifies how many bitcoins were taken.

“The incident has been reported to the relevant authorities and law enforcement and we are cooperating with them as a matter of urgency,” it said. The statement urged users to change their online passwords.

Security questions

The hack will put a spotlight on the security of bitcoin just as the trading community prepares for the currency to start trading on two established U.S. exchanges. Futures for bitcoin will start trading on the Chicago Board Options Exchange on Sunday evening and on crosstown rival CME Group’s platforms later in the month.

That has increased the sense among some investors that bitcoin is gaining in mainstream legitimacy after several countries, like China, tried to stifle the virtual currency.

Bitcoin is the world’s most popular virtual currency. Such currencies are not tied to a bank or government and allow users to spend money anonymously. They are basically lines of computer code that are digitally signed each time they are traded.

People are bidding its price higher even though leading figures in finance and economics are telling them to beware.

Nobel laureate Joseph Stiglitz said last week that bitcoin “ought to be outlawed.” Criticism has also come from the likes of JPMorgan Chase CEO Jamie Dimon and legendary investor Warren Buffett.


But some financial institutions are helping bring bitcoin more into the mainstream.

Starting next week, investors will be able to trade bitcoin futures via the Chicago Board Options Exchange, which is expected to increase interest from hedge funds and big asset managers.

Futures allow traders to bet on the future price of assets like currencies, metals and agricultural commodities.

The Chicago Mercantile Exchange is set to follow with a similar move later in December, while New York’s Nasdaq wants to list bitcoin futures starting in the middle of next year.

“The fact the CME, CBOE and Nasdaq will now all offer bitcoin products lends additional legitimacy,” said Dave Chapman, managing director at Hong Kong’s Octagon Strategy, a digital currency exchange.

Bitcoin is one of many cryptocurrencies, virtual “coins” that are “mined” by computers using complex algorithms.

Its recent rise has been far from smooth. After powering past $11,000 last week, it plunged by more than $2,000, providing a stark reminder of its extreme volatility.

Ever higher?

But cryptocurrency industry insiders are unfazed. They predict bitcoin will soar far higher in the coming months.

Arthur Hayes, CEO of Hong Kong’s Bitmex, an exchange for trading financial instruments based on bitcoin, told CNNMoney last week that he thinks it could hit $50,000 next year.

Octagon’s Chapman is willing to go even further. He believes bitcoin could reach $100,000 before 2018 is out despite a growing number of rival cryptocurrencies that could vie for investors’ attention.

Bitcoin is “the most battle hardened and proven cryptocurrency right now,” he said. “For now, it’s unsurpassable.”