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 Australian founder, Julian Assange. ''In either scenario, WikiLeaks volunteers, under a pre-arranged agreement with Mr 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'' might contain the 15,000 Afghan files whose release WikiLeaks said it had delayed ''as part of a harm minimisation process demanded by our source''.