"Inside WikiLeaks" is billed as a warts-and-all account of Daniel Domscheit-Berg's time as chief programmer and media spokesman for what his tell-all book calls "the world's most dangerous website."

Set for release in 16 countries from Friday, it says that "chaotic" WikiLeaks cannot protect its sources and accuses the "power-obsessed" Assange of being uneconomical with the truth, according to leaked excerpts.

Domscheit-Berg, along with others, left WikiLeaks in September complaining that Assange was being autocratic and that the organisation, ironically for a group on a crusade for openness, was becoming excessively secretive.

WikiLeaks is "far too easy to attack," the 32-year-old told German magazine Stern this week, quoting him as calling Assange "brilliant" but "paranoid" and a "megalomaniac."

Founded in 2006, WikiLeaks caused a storm last year with major document leaks on the wars in Iraq and Afghanistan, as well as publishing US diplomatic cables that have caused Washington and others considerable embarrassment.

Assange, 39, is currently in London fighting extradition to Sweden over allegations of rape and molestation following his arrest by British police in December.