U.S. and British intelligence officials are concerned Edward Snowden might have a “doomsday” cache of highly classified material stored on a data cloud. 

“The worst is yet to come,” one former U.S. official told Reuters.

The collection of documents from the National Security Agency and other agencies includes names of American intelligence officials and those of U.S. allies, seven current and former U.S. officials told Reuters. 

Multiple passwords are needed to unlock the cache, two unidentified sources said, according to the report.

Obama administration officials have said Snowden, the former NSA contractor, might have enough material to leak two years worth of news stories, Reuters reports. 

Only a small portion of the classified documents, however, were allegedly downloaded when Snowden worked for the NSA.

A former senior U.S. official warns Chinese and Russian cryptographers might have the capacity to access the cache, the report said. 

Snowden began leaking classified documents detailing the NSA’s surveillance programs in June. Since August, he has been living at an unknown location in Russia after its government granted him temporary asylum.

He faces espionage charges in the United States. NSA Director Gen. Keith Alexander said in October that Snowden has leaked up to 200,000 documents to journalists this year. 

Alexander offered to resign from his post after the leaks began, The Wall Street Journal reported Monday. The Obama administration, however, rejected his offer.

President Obama has ordered a review of the NSA’s surveillance activities, which is due Dec. 15.