China and the US are set to take action against each other as tensions escalate over trade, cyber hacking and espionage as US senior law enforcement officials identified Beijing as the most serious threat to US national security on Wednesday. China's methods of non-traditional espionage -- including their use of ordinary Chinese expatriates instead of spies at universities and businesses, and intellectual property theft -- were explained by officials from the FBI and departments of Justice and Homeland Security who briefed US lawmakers.
