Coinbase Global said Thursday that it has refused to pay a $20 million ransom demand from cybercriminals who bribed the company’s overseas customer support agents to steal sensitive user data.The cryptocurrency exchange estimated that the incident could cost from $180 million to $400 million,

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.

Coinbase said customer passwords and private keys were protected by its systems, and “at no time were any of the targeted contractors or employees able to access customer funds.”