Intelligence officials in the US and Britain are worried that former US intelligence contractor Edward Snowden, whose revelations in June triggered a massive spying scandal, may have stored a doomsday cache of highly classified documents.
According to seven current and former US officials and other anonymous sources who spoke to Reuters, the collection of the heavily encrypted materials includes names of US and allied intelligence personnel.
Multiple passwords are needed to open the cache and the passwords are in the possession of three unknown people.
One of the sources has described the data as Snowdens insurance policy against any possible physical harm or threat of arrest.
Snowden is believed to have downloaded up to 200,000 classified documents pertained to the US and British governments spying activities. US officials say only a small proportion of the downloaded documents has been disclosed yet.
The worst is yet to come, Reuters quoted one former US official as saying.
Documents disclosed by the American whistleblower since early June have brought to light the scope and scale of Washingtons spying activities across the globe. The documents have shown how the US government collects phone records of all American citizens and tracks the use of US-based Web servers by all people around the world.
Documents having been released by Snowden since June also showed that US spy agencies hacked into the computer systems of other countries diplomatic missions and that National Security Agency has been eavesdropping on phone calls of at least 35 world leaders including that of German Chancellor Angela Merkel, one of Europes most influential leaders.
Yet, according to a February 2012 document obtained by Snowden, the US National Security Agency has vowed to expand its spying powers in order to keep pace with the complexity of the technology and target environments, or the operational expectations levied on NSAs mission.