Former US intelligence contractor Edward Snowden, who blew the whistle on mass government surveillance, has dodged questions about whether he had read all the classified documents he leaked to the public and explained the practical realities of the mass data collection in terms most internet users clearly understand: how easily the government can access your "dick pics".

Snowden made the rare face-to-face interview with comedian and host of satirical program Last Week Tonight John Oliver, who proved once again he does journalism better than many professional journalists. Oliver travelled to Moscow a week ago to speak to Snowden, who sought asylum in Russia after going public with the material.

Oliver, who has fiercely resisted being labelled a journalist in the past, pushed Snowden with a direct and challenging line of questioning in parts of the interview about whether he had actually read all the documents he leaked, asserting that there had been "f...-ups", as Oliver termed them.

Snowden replied that he had evaluated and "understood" all the documents, but would not confirm that he had actually read them.