One of the world's most popular Bitcoin exchanges Bitfinex has been torn apart with hackers making off with around US$65 million (£49 million, A$87 million) in the cryptocurrency.
The Hong Kong company replaced its homepage with a statement on the hack but did not detail losses or the means by which the site was breached.
It said only that withdrawal limits in place at Bitfinex and many other exchanges were mysteriously bypassed.
Community and product development director Zane Tackett said some 119,756 bitcoins were stolen.
"We are investigating the breach to determine what happened, but we know that some of our users have had their bitcoins stolen," the company says.
"We are undertaking a review to determine which users have been affected by the breach.
"While we conduct this initial investigation and secure our environment, bitfinex.com will be taken down and the maintenance page will be left up."
Bitfinex halted all trading, digital token deposits, and withdrawals.
News of the hack sent the value of Bitcoin falling by some 20 percent to about US$540 (£405, A$711)
Tackett disclosed the number of stolen bitcoins to Bitfinex customers via Reddit, and has been fielding scores of inquiries. He says he will post updates to the social network site about the hack tomorrow.
They say no US currency was stolen, and could not confirm details on possible reimbursement for affected customers.
Bitfinex's security firm Bitgo says it has not found any evidence of a breach of its servers during its investigation.
Use of that security company meant customer bitcoin wallets were separated and so limited the scale of the breach.
It followed the US$50 million breach of Etherem which was reversed after a hard fork was enacted.
Police are investigating.
News of the hack broke at around the time Hong Kong was dealing with Typhoon Naida, a storm that saw the territory invoke emergency management plans that emptied the streets and closed most businesses. Some are speculating that the hack somehow took advantage of the weather, but absent information on the precise timing of the hack the theory is at best a tantalising potential plot point in a hypothetical future Bitcoin movie. ®