The trailer to Harry Potter and the Prisoner of Azkaban film was leaked by a fan site:

Industrious, Internet-enabled Harry Potter fans managed to get a sneak preview of a sneak preview of the trailer for the latest movie in the Potter series Wednesday evening. The trailer for the third entry in J.K. Rowling's series, "Harry Potter and the Prisoner of Azkaban," was supposed to make its debut at movie theaters Friday night. Instead, links to video started popping up all over the Internet at around dinner time East Coast time.

IT'S NOT CLEAR how the movie trailer got into the hands of Internet fans, but many Potter sites say the file was posted on Warner Brother's own Web site on Wednesday. The file was quickly removed, but not before it had been copied by viewers, who then made it available on other Web sites. Links to the video, a hefty download at about 14 megabytes, were then plastered on Harry Potter fan sites.

B.K. DeLong, who operates The-Leaky-Cauldron, said there never was an obvious link to the movie on Warner Bros. site. But he was able to figure out the location of the trailer file at about 3 p.m. ET today, simply by altering the file name from the trailer for the second movie.

"Basically, all I did was change HP2 to HP3 ... and it worked. It was too easy," he said. "If they really wanted to keep it from people, they wouldn't have made it that easy."

DeLong didn't know how long the file was posted on Warner Bros. site, but he said it was taken down soon after he placed a link on his Web site.

"They noticed the traffic," he said. [MSNBC.com]