Coinbase disclosed a cybersecurity incident that could cost it up to $400 million.The company's investigation is ongoing, with estimated expenses ranging from $180 million to $400 million for remediation and customer reimbursements.The cyberattack involved data stolen from Coinbase, used for social engineering trickery leading to an attempted $20 million extortion.Coinbase is setting up a $20 million reward fund for information on the cyberattackers, as social engineering fraud rises by 56%.