The U.S. Department of Defense took an estimated 1,500 computers offline Wednesday <A HREF="http://www.cio.com/article/120700/Pentagon_Shuts_Down_Systems_After_Cyberattack">after a security breach</A> within the Office of the Secretary of Defense. "Elements of the OSD unclassified email system were taken offline yesterday afternoon, due to a detected penetration," Secretary of Defense Robert Gates said, according to the transcript of a Thursday press conference. "A variety of precautionary measures are being taken. We expect the system to be online again very soon."

Department of Defense officials had little more to say about the attack, Thursday, and would not confirm the number of systems that had been taken offline.