Coinbase hack could cost $400 million

Coinbase, the leading U.S. cryptocurrency exchange, announced Thursday that a recent hack will cost it up to $400 million to reimburse customers who lost funds. The company said in a statement that it was contacted by hackers who had access to user data. The hacking group demanded $20 million from Coinbase to keep quiet, but the company said it refused to pay and promised to reimburse everyone who was defrauded.

In a filing with the US securities regulator, the SEC , the platform estimated the costs at between "180 and 400 million dollars." But "further examination of potential losses, claims, and potential recoveries could significantly increase or decrease this estimate," it said. Its shares were down 6.5% at 18:00 GMT on Thursday on the New York Stock Exchange.

Coinbase explained that the cybercriminals had "bribed a group of its customer service agents" based overseas. "These insiders abused their access to customer support systems to steal account data from a small subset of customers" and trick them into sending funds, the company detailed.

She clarified that they did not have access to passwords or private keys, and that the data theft affected less than 1% of users. "We are creating a $20 million reward fund for any information leading to the arrest and conviction of the criminals responsible for this attack," she added.