“Very little that China does escapes the notice of the NSA, and virtually every technique it uses has been tracked and reverse-engineered. For years, and in secret, the NSA has also used the cover of some American companies — with their permission — to poke and prod at the hackers, leading them to respond in ways that reveal patterns and allow the United States to figure out, or ‘attribute,’ the precise origin of attacks. The NSA has even designed creative ways to allow subsequent attacks but prevent them from doing any damage. Watching these provoked exploits in real time lets the agency learn how China works.”
Source: Inside the Black Box – By Marc Ambinder | Foreign Policy