The first sign of trouble was a mysterious signal emanating from deep within the U.S. military’s classified computer network. Like a human spy, a piece of covert software in the supposedly secure system was “beaconing” — trying to send coded messages back to its creator.
An elite team working in a windowless room at the National Security Agency soon determined that a rogue program had infected a classified network, kept separate from the public Internet, that harbored some of the military’s most important secrets, including battle plans used by commanders in Afghanistan and Iraq.
via Cyber-intruder sparks response, debate – The Washington Post.