CNN says accusations it faked footage of Palestinians celebrating the US terror attacks are baseless.
Palestinian journalists and officials reportedly claim the footage dates back to 1991, but was passed off as being current.
CNN says a Reuters camera crew filmed the celebrations in East Jerusalem hours after the hijackings.
It says the allegations stem from an email by a Brazilian student.
The Universad Estatal de Campinas-Brasil (Unicamp) says one of its students sent the email after apparently receiving information from a professor at another institution.
Mr Marcio AV Carvalho later realised the claims were false and sent out a correction, says Unicamp.
A spokesman said: "The original message, however, was distributed all over the world, often with many distortions."
A CNN spokesman told reporters: "CNN rejects as baseless and ridiculous an allegation being circulated by email and the internet claiming that CNN televised 10-year-old videotape to illustrate Palestinians celebrating in the wake of the horrific September 11th tragedies in the US.
"CNN applauds Unicamp for setting the record straight. The videotape in question was shot by a Reuters TV camera crew on September 11th."
According to the Islamic Republic News Agency, the Palestinian Journalists' Association has condemned CNN for "journalistic treachery".