Last weekend, U.S. President Barack Obama sat down for a series of meetings with China's newly appointed leader, Xi Jinping. We know that the two leaders spoke at length about the topic du jour -- cyber-espionage -- a subject that has long frustrated officials in Washington and is now front and center with the revelations of sweeping U.S. data mining. The media has focused at length on China's aggressive attempts to electronically steal U.S. military and commercial secrets, but Xi pushed back at the "shirt-sleeves" summit, noting that China, too, was the recipient of cyber-espionage. But what Obama probably neglected to mention is that he has his own hacker army, and it has burrowed its way deep, deep into China's networks.