The "NIPRNET," the Unclassified but Sensitive Internet Protocol Router Network (formerly called the Non-secure Internet Protocol Router Net), is a network of Internet protocol routers owned by the Department of Defense (DOD). Created by the Defense Information Systems Agency (DISA), NIPRNET is used to exchange unclassified but sensitive information between "internal" users. It can thus be distinguished from the Secret Internet Protocol Router Network (SIPRNET), which is used by the DOD to exchange classified information in a totally secure environment. NIPRNET is also increasingly used by the DOD to allow its personnel to gain access the Internet without leaving their own computers open to "reverse entry" by hackers, foreign militaries, terrorists, etc etc.
(Note: on 28 December 2015, we received an email from Terry Davis, the Chief Information Officer at the Department of Defense, which said, "The 'NIPRNET' is now the Non classified Internet Protocol Router Network."