Breach heightens concerns about bitcoin security

TOKYO — 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 Thursday that it is investigating a breach that might have resulted in the theft of about $70 million US 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 would stop operating for 24 hours while it verified how many bitcoins were taken. Wallet is a nickname for an online account.

Miners of bitcoins and other virtual currencies help keep the systems honest by having their computers keep a global running tally of transactions. That prevents cheaters from spending the same digital coin twice.

Online security is a vital concern for such dealings.

In Japan, following the failure of a bitcoin exchange called Mt. Gox, new laws were enacted to regulate bitcoin and other virtual currencies. Mt. Gox shut down in February 2014, saying it lost about 850,000 bitcoins, possibly to hackers.

NiceHash did not respond to an emailed request for more details about the breach.

“The incident has been reported to the relevant authorities and law enforcement and we are co-operating with them as a matter of urgency,” it said in a statement.