From the DoD General Counsel:
This is a Department of Defense (DoD) computer system. This computer system, which includes all related equipment, networks and network devices (specifically including access to the internet), are provided only for official U.S. Government business.
DoD computer systems may be monitored by authorized personnel to ensure that their use is authorized, for management of the system, to facilitate protection against unauthorized access, and to verify security procedures. Monitoring includes "hacker" attacks to test or verify the security of this system against use by unauthorized persons. During these activities, information stored on this system may be examined, copied and used for authorized purposes, and data or programs may be placed into this system. Therefore, information you place on this system is not private.
Use of this DoD computer system, authorized or unauthorized, constitutes consent to official monitoring of this system. Unauthorized use of a DoD computer system may subject you to criminal prosecution. Evidence of unauthorized use collected during monitoring may be provided to appropriate personnel for administrative, criminal or other action. Use of this or any other DoD interest computer system constitutes a consent to monitoring at all times.