A New In-Depth Analysis of Anthem Breach - BankInfoSecurity: "Opening the email launched the download of malicious files to the user's computer and allowed hackers to gain remote access to that computer and dozens of other systems within the Anthem enterprise, ... .
Starting with the initial remote access, the attacker was able to move laterally across Anthem systems and escalate privileges, gaining increasingly greater ability to access information and make changes in Anthem's environment, the investigative report says."