Security → Re: Internet To Be Reinvented By DARPA, Microsoft, Lockheed

According to United States Code Title 17 Circular 92 Section 105: "Copyright protection under this title is not available for any work of the United States Government, but the United States Government is not precluded from receiving and holding copyrights transferred to it by assignment, bequest, or otherwise."

So only if that works is completely done by the United States Government will said work be public domain. If the work is contracted out like this one, the work can be copyrighted but all those little details are setup upfront in the initial contract between the United States Government and the Contractor.