There was a time when journalists used to break hot stories, not be the centre of them.

But the last few years have seen the media under the spotlight itself, often for the wrong reasons. It's probably too soon, and too unsavoury, to have a film about the News Of The World's ignominious band of phone hackers. But Julian Assange, the controversial and fascinating mastermind behind WikiLeaks, is quite the man for a movie makeover.

While the phone hackers represent little more than criminality, the WikiLeaks story has genuine significance, as it epitomises the information revolution that has grown with the internet. For his part, Assange embodies a dichotomy between the laudable expression of freedom of information and the dearth of responsibility that comes with citizen journalism.

Director Bill Condon has dressed this thought-provoking fare as a David and Goliath thriller in which a small band of activist computer geeks take on governments and corrupt businesses in an attempt to make the world a better place - until success and ego undo them.

It opens in Berlin in 2007, when Assange (Benedict Cumberbatch), computer hacker turned political activist, meets Daniel Domscheit-Berg (Daniel Bruhl), a rebellious programmer in need of a cause. Assange gives him one: a freedom of information website that offers a platform for whistleblowers, their identities "concealed in code", to expose government wrongdoing and corporate crimes.

With his flowing white locks and lispy voice, scruffy anorak and poor social skills, Assange seems like a man from another planet (like Facebook's Mark Zuckerberg, here's another web visionary as geeky outsider). But he knows how to spin a line and create an aura of mystique around himself. He also means business. The idealist and the pragmatist join forces.

Thereafter, it's a chronological account of their successes - the exposure of a crooked Swiss bank and murderous Kenyan police, the "collateral murder" video showing the killing of civilians by US helicopters in Iraq. They attract the attention of the mainstream press, notably The Guardian, which starts to sniff around a ready-made scoop machine. Then WikiLeaks finds itself the recipient of thousands of US military documents and diplomatic briefings. And the game changes.

The film doesn't shy away from the ethical questions - notably around Assange's refusal to edit any of the material flowing into his site, thus risking the lives of people in sensitive positions mentioned in those leaks. The story's dramatic core is the growing schism between Assange and Domscheit-Berg; between recklessness and responsibility. Around them the issues are explored through the characterisations of the British journalists and the US state officials who must suddenly protect not just their reputations, but also their sources' lives.

Condon is an interesting director, one moment helming the teen twaddle of Twilight, the next the storming entertainment of Dreamgirls or thoughtful, edgy films like Gods And Monsters and Kinsey. The Fifth Estate falls into the latter category, offering a contemporary morality tale about the battle between truth and responsibility, idealism and hubris, presented with pace and visual panache.

Just weeks after his Nikki Lauda in Rush appeared in cinemas, Bruhl offers more proof of his versatility. He's one of a sterling number of supporting cast members. But at the heart of the film is another fine performance by Cumberbatch, who presents Assange as campaigning journalist, geek and egocentric, self-styled messiah, all in one package. Angel or demon? You decide.