(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.

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