Studios want to stop actors from leaking film information on social network sites, and are inserting clauses in their contracts forbidding them.

Stars affected include Cameron Diaz and Mike Myers, who are due to make a Shrek follow-up next year for studio DreamWorks.

According to The Hollywood Reporter, the entertainment newspaper, a recent talent contract from Disney includes a new clause forbidding confidentiality breaches via "interactive media such as Facebook, Twitter, or any other interactive social network or personal blog."

And at DreamWorks, a contract cautions writers not to jump the gun on studio press releases via “a social networking site, blog or other Internet-type site.”

“This is just the beginning,” a talent lawyer told the newspaper. “Hollywood has a long history of controlling what talent says in the media. This is just a new area of media that hasn’t been controlled yet.”

The move comes after American Idol judge Paula Abdul dramatically resigned this year on Twitter. Her announcement was followed by an official reaction from Fox News wishing her well.

Ryan Seacrest, the American Idol presenter, was criticised after he broke the news of NBC's former co-chairman Ben Silverman’s resignation from the company on his Twitter feed.

Heroes actor Greg Grunberg also caused controversy when he posted a tweet during filming for the last episode of season three.

"Tough to say goodbye to crew not knowing if any or all of us will return next year," he wrote.

After being inundated with messages from fans who thought it meant the show would not be coming back Grunberg had to post a new tweet to clarify that the show "IS coming back [for a fourth season] but some crew take other jobs, so it's tough."

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