A "pirated" copy of the latest Harry Potter film on the internet has turned out to be an empty decoy, according to the movie's film studio AOL Time Warner.

There were reports that pirated copies were showing up online, with one site apparently showing the film had been downloaded more than 500 times.

But AOL Time Warner said it had opened a copy of Harry Potter and the Chamber of Secrets located on the internet and found it to be an empty decoy.

The company had earlier said the copy that had been discovered was of poor quality.

The film is the second in the series by JK Rowling

The film - which cost more than $125m (�78.6m) to make - was viewed by British audiences in sneak previews over the weekend before its wider release.

Industry experts believe a pirated version of the film could have been made then.

Theft

AOL Time Warner described the illegal copying and distribution of movies as "theft" in a statement released on Tuesday.

"Warner Bros takes the threat of internet piracy very seriously," it said.

The company said it would employ all legal means to combat the threat.

'Not enjoyable'

Industry experts said that having a movie leaked to the web before its opening is not unusual, especially with highly anticipated films - it has already happened with Spider-Man and the Star Wars franchise.

Market research firm Viant Media estimates that up to 500,000 film files a day are traded on the internet through file-sharing services like Kazaa and Morpheus.

Downloading movies, either legitimately or through the black market, can take several hours - much longer than it takes to download music files.

And most movie-goers say they do not enjoy watching a film on a computer.

They are usually grainy, jumpy versions, filmed using a handheld camera at pre-premiere screenings.