"Details are still sparse, but both the LA Times and the U.S.
News and World Report are reporting that the intrusion was severe
enough to raise the INFOCON status, the information security
equivalent of the DEFCON alert, and also necessitate the briefing
of the president. We also don’t know the source of the
attack, but signs point to state rather than non-state actors, with
the most popular contenders being either Russia or China."
Even the linked news articles are shy on what operating
systems are affected; however, a bit of Googling reveals that
agent.btz is a Windows worm--ed.