The scam, known as Business Email Compromise Scheme (BEC), involved gaining access to corporate email accounts, and sending fraudulent emails to unwitting employees, who were instructed to wire funds to a bank acccount set up by the defendant. Access to corporat email was accomplished usig computer instrusion or social engineering techniques. Associates then converted the money to Bitcoin, which was sent to Poole's virtual wallet.
The exact amount of loss is not specified in the Criminal Complaint, but appears to be in the tens of millions of dollars. One company lost $15.2m. The text messages and correspondence between the defendant and his co-conspirators appears in the Criminal Complaint, which may be accessed here.