When Edward Snowden leaked American intelligence secrets the whole world became aware of the extent of US-UK surveillance of global phone and internet traffic. Have the revelations flagged up a corrosive infringement of individual liberty, or undermined efforts to protect the world from terrorism? Hardtalk speaks to journalist, Glenn Greenwald - the man who broke the Snowden story. His mission, he says, is to hold power to account. Is this a journalistic crusade that's gone too far?