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 reported in a Securities and Exchange filing Thursday the company received an email on May 11 from an “unknown threat actor” that claimed to have stolen sensitive information from less than 1% of its monthly users, including data related to “customer service and account management systems.”

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