It may be the most stunning and creative attack ad yet for a 2008 presidential candidate -- one experts say could represent a watershed moment in 21st century media and political advertising. Yet the groundbreaking 74-second pitch for Democratic Illinois Sen. Barack Obama, which remixes the classic "1984" ad that introduced Apple computers to the world, is not on cable or network TV, but on the Internet.

And Obama's campaign says it had absolutely nothing to do with the video that attacks one of his principal Democratic rivals, New York Sen. Hillary Rodham Clinton. Indeed, the ad's creator is a mystery, at least for now.

The compelling "Hillary 1984" video recently introduced on YouTube represents "a new era, a new wave of politics ... because it's not about Obama," said Peter Leyden, director of the New Politics Institute, a San Francisco-based think tank on politics and new media. "It's about the end of the broadcast era."

The video is a sophisticated new take on director Ridley Scott's controversial Apple ad that caused shock waves with its premiere during the 1984 Super Bowl, and shows the same blond young female athlete running with a sledgehammer toward a widescreen -- where an ominous Big Brother figure drones to a mass of zombielike followers.

But this time, the woman is wearing an iPod -- and has her candidate's slogan on her chest. And the Big Brother -- whose image she defiantly smashes with a wave of her sledgehammer -- is Clinton, the Democratic presidential front-runner. The tagline for the attack: "On Jan. 14, the Democratic primary will begin. And you'll see why 2008 won't be like 1984." An updated Apple symbol -- transformed into an O -- is followed by the dramatically emerging logo: BarackObama.com.

The ad is proof that "anybody can do powerful emotional ads ... and the campaigns are no longer in control," Rosenberg said. "It will no longer be a top-down candidate message; that's a 20th century broadcast model."

It also dramatizes that today, political activists with the Internet as their ammunition have gone from being "just donors to the cause," he said, "to being partners in the fight. And they don't have to wait for permission."

But while the medium is clearly more grassroots, political campaigns have not been averse to having an outside or independent voice -- witness the efforts of the Swift Boat Veterans for Truth in the 2004 presidential race against Democratic Sen. John Kerry -- delivering ads that are tougher and meaner than the candidates might launch on their own.