On March 14, 2013, the Romanian hacker nicknamed Guccifer broke into the email account of Clinton confidant Sid Blumenthal and made Clinton’s private email address public. Cheryl Mills was Clinton’s chief of staff until January 2013, when both she and Clinton left the State Department. But Mills continues to assist Clinton, and in August 2016 she will mention in written answers to a Freedom of Information Act (FOIA) lawsuit that she was concerned at this time how the Guccifer hack could impact the running of Clinton’s private email server.
She says she discussed the issue with Bryan Pagliano, Clinton’s computer technician “in or around March 2013, when the email account of Sidney Blumenthal was compromised by a hacker known as Guccifer. As I recall, these discussions involved whether this event might affect Secretary Clinton’s email.”
Clinton changed her email address several days after the Guccifer hack was discovered. However, the server continued to operate and her new email address was also hosted on the same server. It is still unknown whether Pagliano or anyone else took any other security steps in response to the hack. (Politico, 8/10/2016)