The internet has made it possible to share all of the world’s knowledge. Sometimes that is a good thing, whether we’re able to track down just the exact item we want at the lowest possible price or make micro-loans to entrepreneurs in emerging economies, tracking down lost friends and family, or crowd-sourcing complex problems. Sometimes it is a bad thing as when personal or embarrassing information we think of as private becomes very public. In essence, it is great when we have access to other people’s information; not so great when they have access to ours.

So, who decides what stays secret? This brilliant documentary from Alex Gibney (“Enron: The Smartest Guys in the Room,” “Taxi to the Dark Side”) explores that question through the stories of two mesmerizing personalities, itself a meta-narrative as the documentarian is exposing the secrets of the secret-sharers.

In 1989, a worm infected more than 300,000 computer systems throughout the world.  Like a real-life “WarGames,” it was the work of a smart-alecky teenager.  It was Julian Assange, who would grow up to found Wikileaks, a website set up to receive and make public confidential material, protecting the people — whistle-blowers or thieves, depending on your point of view — who provided it.

And then there was Bradley Manning, a private in the U.S. military.  Like Assange, he had exceptional computer skills.  He had personal and philosophical reasons to be angry at the U.S. government.  He was struggling with issues of sexuality and gender identity.  He was isolated.  And no one thought he was a risk.

The combination was like gasoline and a match, or maybe the Enola Gay and Fat Man.  This is the story of two men who think of themselves as following in the tradition of Daniel Ellsberg in exposing the secrets of military operations, while at the same time they are exposing the vulnerability of our systems for keeping information restricted.  If what is released brings to light shameful violations of core principles of honor and integrity, is it honorable to make it public?  What if it exposes our operations to our enemies?

Gibney’s portrayal is itself a model of even-handed, serious consideration of these issues, as highly principled and professional organizations (the New York Times and The Guardian) play a responsible filtering function in sorting through “a mountain of secrets dumped into the public domain” and providing perspective and judgment, and as Assange and Manning themselves find their own secrets exposed to the world and are charged with crimes that have led to Manning’s being imprisoned under the severest of conditions and Assange essentially a prisoner unable to leave the Ecuadorian embassy in London without being extradited to Sweden to be prosecuted for sexual assault.  The film explains that 9/11 was a “watershed moment for the world of secrets,” for both keepers and sharers.  There was an unprecedented need to track terrorists and that meant an unprecedented sharing of information.  And that meant that a young private had easy access to endless classified material.  It was routine for the bored young soldiers to bring in blank CD’s to download music while they worked.  It appeared that is what he was doing, but he was downloading hundreds of thousands of documents.

“Was it once not considered patriotic to stand up to our government when it’s wrong?” someone asks.  Well, maybe.  But not at the time.  There is a lot of blaming the messenger for the bad news in this movie, perhaps most sickeningly in the attacks on the women who have accused Assange of abuse.  And, as is so often the case, heroes are not the lantern-jawed Boy Scouts we want them to be.  That’s in the movies.  No fictional story could have come up with the almost sociopathic arrogance of Assange, who likes to brag that “I’m a combative person so I like crushing bastards” or the anguished Manning, whose betrayal of his country is matched by his betrayal by the one person he trusted, an online-only friend who gave his name to the authorities.

The government will always try to control information, whether it is George W. Bush prohibiting the release of images of coffins of dead soldiers or protecting the names of CIA field personnel.  The government will aways try to get information, whether it is tracking down Bin Laden or seizing the phone records of reporters.  This thoughtful, balanced, essential examination of the clash between privacy and transparency exemplifies the best that intelligence, dedication, and honor can bring to illuminating these issues — and the devastating impact of leaving those decisions to the arrogant and unstable.

Parents should know that this film includes some images of war violence and discussions of sexual assault and gender identity issues.

Family discussion: How do we “destroy corruption?”  How do we achieve “a more civilized and just society?”  Is there a way to keep secrets?  Should there be?

If you like this, try: “The Most Dangerous Man in the America: Daniel Ellsberg and the Pentagon Papers” and “Gatekeepers,” with the former heads of the Israeli secret service revealing their own most classified secrets about shameful episodes in the conduct of their efforts to keep Israel safe.