And, as usual, humans are the weakest link.The hacked ones were part of the DNC's virtual network with multiple user computers and servers with multiple access points to the network. Once they phished a user for his password they were able to gain access to the network and it's resources. The Clinton servers were real machines locked away in a computer closet. No virtual access made them much more secure, plus it was a stand alone email server and not part of the DNC or any other network with multiple users and access points.