(Reuters) - British and U.S. intelligence officials say they are worried about a "doomsday" cache of highly classified, heavily encrypted material they believe former National Security Agency contractor Edward Snowden has stored on a data cloud.
The cache contains documents generated by the NSA and other agencies and includes names of U.S. and allied intelligence personnel, seven current and former U.S. officials and other sources briefed on the matter said.
The data is protected with sophisticated encryption, and multiple passwords are needed to open it, said two of the sources, who like the others spoke on condition of anonymity to discuss intelligence matters.
The passwords are in the possession of at least three different people and are valid for only a brief time window each day, they said. The identities of persons who might have the passwords are unknown.
Spokespeople for both NSA and the U.S. Office of the Director of National Intelligence declined to comment.
One source described the cache of still unpublished material as Snowden's "insurance policy" against arrest or physical harm.
U.S. officials and other sources said only a small proportion of the classified material Snowden downloaded during stints as a contract systems administrator for NSA has been made public. Some Obama Administration officials have said privately that Snowden downloaded enough material to fuel two more years of news stories.
"The worst is yet to come," said one former U.S. official who follows the investigation closely.