It seems that Hillary Clinton's team intentionally ignored security markings on highly sensitive information.
The FBI is investigating whether members of Hillary Clinton's inner circle "cut and pasted" material from the government's classified network so that it could be sent to her private email address, former State Department security officials say.
Clinton and her top aides had access to a Pentagon-run classified network that goes up to the Secret level, as well as a separate system used for Top Secret communications.
The two systems -- the Secret Internet Protocol Router Network (SIPRNet) and the Joint Worldwide Intelligence Communications System (JWICS) -- are not connected to the unclassified system, known as the Non-Classified Internet Protocol Router Network (NIPRNet). You cannot email from one system to the other, though you can use NIPRNet to send emails outside the government.
Somehow, highly classified information from SIPRNet, as well as even the super-secure JWICS, jumped from those closed systems to the open system and turned up in at least 1,340 of Clinton's home emails -- including several the CIA earlier this month flagged as containing ultra-secret Sensitive Compartmented Information and Special Access Programs, a subset of SCI.