According to this article on Yahoo, sensitive US military files were found openly available online during a survey conducted by Associated Press.
Detailed schematics of a military detainee holding facility in southern Iraq, Geographical surveys and aerial photographs of two military airfields outside Baghdad, and Plans for a new fuel farm at Bagram Air Base in Afghanistan were among the sensitive materials found generally available online.

The military calls it "need-to-know" information that would pose a direct threat to U.S. troops if it were to fall into the hands of terrorists. It's material so sensitive that officials refused to release the documents when asked.