Bitstamp, a major Bitcoin exchange, went offline on Monday after the service discovered that one of its operational wallets was possibly compromised, according to a notice on the site.
The data breach is believed to have occurred Jan. 4, although the site noted that only a “small fraction” of customers' Bitcoins are stored in online systems and could have been affected. Bitstamp also assured customers that its offline reserve contains plenty of Bitcoins, enough to cover any that might have been compromised.
“Bitstamp takes our security and soundness very seriously,” the company's notice said. “In an excess of caution, we are suspending service as we continue to investigate. We will return to service and amend our security measures as appropriate.”
Deposits should not be made to previously issued addresses; however the company's reserves will cover deposits made before Jan. 5.UPDATE: In a statement to SCMagazine.com, Bitstamp CEO Nejc Kodrič confirmed that the breach "represents a small fraction of Bitstamp's total Bitcoin reserves, the overwhelming majority of which are held in secure offline cold storage systems" and assured customers that their Bitstamp balances held prior to the temporary suspension of services will be honored in full. The breach resulted in a loss of less than 19,000 Bitcoins, or slightly more than $5 million.
UPDATE 2: Bitstamp services remained suspended on Wednesday, two days after some of the exchange's operational wallets were compromised. However, the company did tell SCMagazine.com in a statement that it's working to bring its new site online in "the coming days."