December 2015: The FBI warns the DNC (Democratic National Committee) that it is a target of a hacker attack.

According to a July 2016 Yahoo News article, the FBI contacts the DNC in late 2015 and tells their IT (information technology) staffers that there has been a hacking attack on the DNC’s computer network. The FBI provides no details, such as who the hackers might be.

It will later be discovered that a hacker broke into the DNC network in the summer of 2015. Despite the FBI warning, the hacker won’t be ejected from the network until around June 2016. (Yahoo News, 7/29/2016)