Legality of Intrusion-Detection System to Protect Unclassified Computer Networks in the Executive Branch, Memorandum Opinion for an Associate Deputy Attorney General [August 14, 2009] [open pdf - 35KB]
"Operation of the EINSTEIN 2.0 intrusion-detection system complies with the Fourth Amendment to the Constitution, title III of the Omnibus Crime Control and Safe Streets Act of 1968, the Foreign Intelligence Surveillance Act, the Stored Communications Act, and the pen register and trap and trace provisions of chapter 206 of title 18, United States Code, provided that certain log-on banners or computer-user agreements are consistently adopted, implemented, and enforced by executive departments and agencies using the system. Operation of the EINSTEIN 2.0 system also does not run afoul of state wiretapping or communications privacy laws."
U.S. Dept. of Justice: http://www.justice.gov/