WASHINGTON DC, United States?Whistleblower website WikiLeaks has posted a mysterious encrypted "insurance file," touching off speculation about what it contains.

Wired magazine said the 1.4-gigabyte "insurance file" appeared on WikiLeaks' "Afghan War Diary" page several days after the site released tens of thousands of classified documents related to the war in Afghanistan.

Cryptome, another whistleblower site, said it may have been "pre-positioned for public release" in the event of a "takedown" of WikiLeaks by US authorities or if something happens to its founder, Julian Assange, an Australian national.

"In either scenario, WikiLeaks volunteers, under a prearranged agreement with Assange, could send out a password or passphrase to allow anyone who has downloaded the file to open it," Wired said.

The file is also available on a file-sharing site in addition to the WikiLeaks page.

Cryptome.org speculated the "insurance file" may contain the 15,000 Afghan files whose release WikiLeaks said it had delayed "as part of a harm minimization process demanded by our source."

WikiLeaks has never identified the source of the Afghan files but suspicion has fallen on Bradley Manning, a US Army intelligence analyst who is under arrest for allegedly leaking video of a 2007 US Apache helicopter strike in Baghdad in which civilians died.

Wired said the "insurance file" may contain more material from Manning, including war logs from Iraq, video from Afghanistan, and 260,000 US State Department cables.