The internet is the "greatest spying machine the world has ever seen" and is not a technology that necessarily favours the freedom of speech, the WikiLeaks co-founder, Julian Assange, has claimed in a rare public appearance.

Assange acknowledged that the web could allow greater government transparency and better co-operation between activists, but said it gave authorities their best ever opportunity to monitor and catch dissidents.

"While the internet has in some ways an ability to let us know to an unprecedented level what government is doing, and to let us co-operate with each other to hold repressive governments and repressive corporations to account, it is also the greatest spying machine the world has ever seen," he told students at Cambridge University. Hundreds queued for hours to attend.

He continued: "It [the web] is not a technology that favours freedom of speech. It is not a technology that favours human rights. It is not a technology that favours civil life. Rather it is a technology that can be used to set up a totalitarian spying regime, the likes of which we have never seen. Or, on the other hand, taken by us, taken by activists, and taken by all those who want a different trajectory for the technological world, it can be something we all hope for."

Assange also suggested that Facebook and Twitter played less of a role in the unrest in the Middle East than has previously been argued by social media commentators and politicians.

He said: "Yes [Twitter and Facebook] did play a part, although not nearly as large a part as al-Jazeera. But the guide produced by Egyptian revolutionaries … says on the first page, 'Do not use Facebook and Twitter', and says on the last page, 'Do not use Facebook and Twitter'.

"There is a reason for that. There was actually a Facebook revolt in Cairo three or four years ago. It was very small … after it, Facebook was used to round-up all the principal participants. They were then beaten, interrogated and incarcerated."

Assange said that cables released by WikiLeaks played a key role in both fomenting unrest in the Middle East and forcing the US government not to back former Egyptian president Hosni Mubarak.

Assange said diplomatic cables concerning US attitudes to the former Tunisian regime had given strength to revolutionary forces across the region.

"The Tunisian cables showed clearly that if it came down to it, the US, if it came down to a fight between the military on the one hand, and Ben Ali's political regime on the other, the US would probably support the military."

He continued: "That is something that must have also caused neighbouring countries to Tunisia some thought: that is that if they militarily intervened, they may not be on the same side as the United States."

Assange, who is appealing against his extradition to Sweden on alleged sex charges, said the WikiLeaks releases had also forced the US to drop their tacit support of Mubarak.

"As a result of releasing cables about Suleiman [the vice-president of Egypt under Mubarak], the US and Israel's preferred option for regime takeover in Egypt, as a result of releasing cables about Mubarak's approval of Suleiman's torture methods, it was not possible for Joseph Biden to [repeat his earlier claim that Mubarak was not a dictator]. It was not possible for Hillary Clinton to publicly come out and support Mubarak's regime."

Responding to a question about Bradley Manning, the US soldier incarcerated for allegedly leaking classified information, Assange said: "We have no idea whether he is one of our sources. All our technology is geared up to make sure we have no idea."

He expressed sympathy for Manning. "He is in a terrible situation. And if he is not connected to us, [then] he is there as an innocent … and if he is in some manner connected to our publications, then of course we have some responsibility. That said, there is no allegation that he was arrested as the result of anything to do with us. The allegation is that he was arrested as a result of him speaking to Wired magazine in the United States."

Assange also criticised the New York Times, which he claimed had suppressed stories about secret American military activity in Afghanistan.