The US intelligence whistleblower Edward Snowden has warned that entire populations, rather than just individuals, now live under constant surveillance.



“It's no longer based on the traditional practice of targeted taps based on some individual suspicion of wrongdoing,” he said. “It covers phone calls, emails, texts, search history, what you buy, who your friends are, where you go, who you love.”



Snowden made his comments in a short video that was played before a debate on the proposition that surveillance today is a euphemism for mass surveillance, in Toronto, Canada. The former US National Security Agency contractor is living in Russia, having been granted temporary asylum there in June 2013.



The video was shown as two of the debaters – the former US National Security Administration director, General Michael Hayden, and the well-known civil liberties lawyer and Harvard law professor, Alan Dershowitz – argued in favour of the debate statement: “Be it resolved state surveillance is a legitimate defence of our freedoms.”

Opposing the motion were Glenn Greenwald, the journalist whose work based on Snowden’s leaks won a Pulitzer Prize for the Guardian last month, and Alexis Ohanian, co-founder of the social media website Reddit.

The Snowden documents, first leaked to the Guardian last June, revealed that the US government has programs in place to spy on hundreds of millions of people’s emails, social networking posts, online chat histories, browsing histories, telephone records, telephone calls and texts – “nearly everything a typical user does on the internet”, in the words of one leaked document.



Greenwald opened the debate by condemning the NSA’s own slogan, which he said appears repeatedly throughout its own documents: “Collect it all.”



“What is state surveillance?” Greenwald asked. “If it were about targeting in a discriminate way against those causing harm, there would be no debate.



“The actual system of state surveillance has almost nothing to do with that. What state surveillance actually is, is defended by the NSA's actual words, that phrase they use over and over again: 'Collect it all.’ ”

Dershowitz and Hayden spent the rest of the 90 minutes of the debate denying that the pervasive surveillance systems described by Snowden and Greenwald even exist and that surveillance programs are necessary to prevent terrorism.

“Collect it all doesn't mean collect it all!” Hayden said, drawing laughter.

Greenwald sparred with Dershowitz and Hayden about whether or not the present method of metadata collection would have prevented the terrorist attacks on 11 September, 2001.

While Hayden argued that intelligence analysts would have noticed the number of telephone calls from San Diego to the Middle East and caught the terrorists who were living illegally in the US, Greenwald argued that one of the primary reasons the US authorities failed to prevent the attacks was because they were taking in too much information to accurately sort through it all.

Before the debates began, 33% of the audience voted in favour of the debate statement and 46% voted against. It closed with 59% of the audience siding with Greenwald and Ohanian.

• This article was amended on 6 May 2014 to correct the date of the terrorist attacks that happened on 11 September, 2001, from 2011 as the original said.