Coinbase forecast a hit of $180 million to $400 million from a cyberattack that breached account data of a "small subset" of its customers, the crypto exchange said in a regulatory filing on Thursday.

Coinbase, the largest cryptocurrency exchange based in the U.S., said Thursday that criminals had improperly obtained personal data on the exchange’s customers for use in crypto-stealing scams and were demanding a $20 million payment not to publicly release the info.

Cryptocurrency exchange Coinbase said it had been hacked by cyber thieves demanding a $20 million ransom not to publicly release stolen customer data.

The cryptocurrency exchange estimated preliminary expenses of $180 million to $400 million for remediation costs and voluntary customer reimbursements.