WikiLeaks founder Julian Assange said in a recent interview that he is holding back "insurance files" which could embarrass Rupert Murdoch and his international media empire at News Corporation.
The secrets website was also holding of over 500 US State Department cables about one broadcasting organization in particular, he added.
Assange made the disclosure while speaking to New Statesman, saying the files "will be released" if something happens to him or his organization.
"There are 504 US embassy cables on one broadcasting organisation and there are cables on Murdoch and News Corp.," he said.
The files "speak more of the same truth to power," he added.
In early December, WikiLeaks promised that it would release its full cache of secrets if Assange was arrested or killed.
The organization has taken the precaution of posting a big, 1.4-gigabyte file encrypted with a 256-digit key they claimed was unbreakable.
Titled "insurance.aes256", the file was big enough to contain all the US cables said to be in WikiLeaks' possession.
The encryption makes it unreadable until the key is supplied -- at which time all its contents would be available to those who downloaded it from peer-to-peer file sharing networks.
Appearing on the BBC, Assange's lawyer defended the move. "They need to protect themselves," Mark Stephens said. "This is what they believe to be a thermo-nuclear device effectively in the electronic age."
Assange was detained on a warrant seeking his extradition to Sweden, where he was sought for questioning related to allegations of sexual assault. WikiLeaks has not yet released the key.
The US Department of Justice was investigating whether it could charge Assange with espionage or conspiracy, but no formal charges had been issued.
"I think what's emerging in the mainstream media is the awareness that if I can be indicted, other journalists can, too," the controversial whistleblower told New Statesmen.
"Even the New York Times is worried," he said. "This used not to be the case. If a whistleblower was prosecuted, publishers and reporters were protected by the First Amendment, which journalists took for granted. That's being lost."