Maj. Gen. Richard Webber, commander of Air Force Network Operations, issued the Dec. 3 "Cyber Control Order" which directs airmen to "immediately cease use of removable media on all systems, servers and stand-alone machines residing on SIPRNET," the Defense Department's secret network, Wired Magazine reported.
Similar orders have been issued to the military's other branches, Wired said.
"Unauthorized data transfers routinely occur on classified networks using removable media and are a method the insider threat uses to exploit classified information. To mitigate the activity, all Air Force organizations must immediately suspend all SIPRNET data transfer activities on removable media," the order said.
The ban is one of a number of moves the Defense Department is making to prevent further disclosures of secret information in the wake of the WikiLeaks revelations.
A military source familiar with the networks says it will make troops' jobs harder, as classified computers are often disconnected from the network and a DVD or a thumb drive is often the easiest way to get information from one machine to the next.
"They were asking us to build homes before," the source says. "Now they're taking away our hammers."
The order acknowledges the ban will make life harder for some troops.
"Users will experience difficulty with transferring data for operational needs which could impede timeliness on mission execution," the order admits.
But "military personnel who do not comply may be punished under Article 92 of the Uniformed Code of Military Justice," the armed forces' regulation covering failure to obey orders and dereliction of duty under which violators "shall be punished as a court-martial may direct."