Instead of paying the $20 million ransom, Coinbase offered the same amount of money for information leading to the attackers.

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.”

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.”