It's the biggest intelligence breach in U.S. history-the leaking of more than half-a-million classified documents on the Wikileaks website in the spring of 2010. Behind it all, stand two very different men: Julian Assange, the Internet activist and hacker who published the documents, and an Army intelligence analyst named Bradley E. Manning, who's currently charged with handing them over. Private Manning allegedly leaked the secret cables -- along with a controversial video -- in the hope of inciting "worldwide discussion, debates and reforms." Assange's stated mission has been to force the U.S. and other governments into maximum transparency through his whistle-blowing website. Through in-depth interviews with Manning's father, Assange, and others close to the case, veteran FRONTLINE correspondent Martin Smith tells the full story behind the leaks. He also reports on the U.S. government's struggle to protect national security information in a post 9/11 world.