Cryptocurrency exchange Coinbase said Thursday cyber criminals stole customer data and demanded a $20 million payment from the company to not publicly release the sensitive information. The group

Crypto exchange Coinbase has disclosed a significant cyber attack that could cost the company between $180m (£135m) and $400m (£300m), after hackers breached account data belonging to a “small subset” of its users.

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.