UK-based Bitstamp, the second largest bitcoin exchange for US dollars, suspended operations on Monday, following evidence that online thieves had stolen up to 19,000 BTC—approximately $5.2 million—from its operational store of bitcoins.
The company alerted its users of the possible attack on Monday and warned against transferring any bitcoins to the service’s old bitcoin deposit addresses. Early the following morning, Bitstamp revealed that the attack affected fewer than 19,000 bitcoins. The actual attack appeared to have occurred on Sunday, January 4, when attackers compromised the company’s operational funds, also known as the “hot wallet."
“Thank you all for your patience, we are working diligently to restore service,” Nejc Kodrič, the co-founder and CEO of Bitstamp, tweeted on Monday, adding, “To restate: the bulk of our bitcoin are in cold storage, and remain completely safe.”