Doctor Who fans are being warned not to be fooled by people posing as some of the show's main stars on the internet.
The makers of the series put out the warning after spotting several cases of people pretending to be David Tennant in internet chatrooms and forums.
Others set up fake profiles for the cast, including new Doctor Matt Smith, on social networking sites.
A spokesman said: "Do not be fooled by these impersonators - it will never be David Tennant or Matt Smith online."
He said neither of the stars used social networking websites, chatrooms or forums.
"They wouldn't want fans to think that anyone who uses these are talking to the real actors," he added.
"For their own safety, we would strongly advise all Doctor Who fans to ignore any such postings."