The U.S. secretly traced a massive cyberespionage operation against the 2008 presidential campaigns of Barack Obama and John McCain to hacking units backed by the People’s Republic of China, prompting high level warnings to Chinese officials to stop such activities, U.S. intelligence officials tell NBC News. …

The goal of the campaign intrusion, according to the officials: to export massive amounts of internal data from both campaigns—including internal position papers and private emails of key advisers in both camps.

“Based on everything I know, this was a case of political cyberespionage by the Chinese government against the two American political parties,” said Dennis Blair, who served as President Obama’s director of national intelligence in 2009 and 2010. “They were looking for positions on China, surprises that might be rolled out by campaigns against China.”