tech-savvy teams tracked file-sharing sites on the internet for any evidence of pirated copies.

When the film opened in Australia and New Zealand, ushers in every cinema were given night-vision goggles so they could scour the audience for people who might be using camcorders. When the film came to the US two days later, the same tactic caught a member of the audience taping the film at a 9.40am showing in Kansas.

Warner Bros believes the operation was so successful that the first dodgy copy didn't hit the internet until 38 hours after the film's release in Australia. They are convinced this delay was critical in helping the film to its record-breaking $158m first weekend.

"It's so important to try to protect the first weekend because it prevents the pirate supply chain

from starting," says Darcy Antonellis, president of Warner's distribution and technical operations. "A day or two becomes really, really significant. You've delayed disc manufacturing. That then delays distribution, which then delays those discs from ending up on street corners for sale."

Not everyone is convinced. On the website techdirt.com, one writer suggested that the millions Warner Bros spent on their anti-piracy efforts were wasted because there was so much excitement about The Dark Knight everyone wanted to see it in cinemas anyway.

"Until the movie industry realizes that it's the experience they're selling, beyond just the content," he said, "it sounds like they're going to be throwing a lot more money down this anti-piracy hole than they're actually 'losing' to piracy."