April and May 2011: Clinton and her top aides are warned again to minimize the use of personal emails for business due to hacker attacks.

In March 2011, State Department security officials warned Clinton and other senior officials that there was a “dramatic increase” in hacker attacks specifically targeting senior US officials. It concluded, “We urge department users to minimize the use of personal web email for business.”

This is followed by a cybersecurity briefing in April 2011 and then another one in May. Clinton’s immediate staff and other top officials attend the briefings, but it is not clear if Clinton herself does. However, after Clinton ends her term in 2013, a copy of a classified presentation used during one of the briefings will be found in her papers. It contains warnings similar to the March 2011 warning. (US Department of State, 5/25/2016)