The US and its allies fear that declared NSA spy Edward Snowden may be in possession of what they are calling a "doomsday cache," which contains highly classified encrypted data.
Unnamed US officials say they believe Snowden has the data stored on a data cloud.
Current and former intelligence officials briefed on the matter say the "doomsday cache" contains documents generated by the NSA and other agencies, which includes names of US and allied intelligence personnel.
According to Reuters, two of the officials believe the data's encryption is highly sophisticated and several passwords are needed to access it.
The anonymous sources said the passwords are only valid for a short period of time each day and are known by a select few, who are unidentified.
No official comment was made by either the NSA or US Office of the Director of National Intelligence.
One of the sources describes this so-called "doomsday cache" as Snowden's "insurance policy" in case he gets arrested or harmed in any way.
Officials suggest that the former NSA contractor could have instructed someone to release the information if something was to happen to him.
Obama administration officials say privately that Snowden has access to enough information to fuel news stories for the next two years.
"The worst is yet to come," said one former US official who follows the investigation closely.
Edward Snowden is believed to have stolen anywhere from 50,000 to 200,000 documents from the NSA and British Intelligence during his time at the agency. So far he has released over 500 of them, according to the website Cryptome.
The question becomes finding where the "doomsday cache" is stored, as it is believed that China and Russia have agents which have the capability of deciphering the encryption if the data is found.
Snowden's revelations have brought to light the spying activities undertaken by the NSA on regular Americans via social media, email services, and phone tapping.
The Obama administration has been heavily criticized in Europe after the discovery that the intelligence agency was caught tapping German Chancellor Angela Merkel's private cell phone.
Some of the documents Snowden is believed to have in his possession contain names and resumes of employees working for the British agency, the Government Communications Headquarters (GCHQ).
"If anything happens at all to Edward Snowden, he has arranged for them to get access to the full archives," Glenn Greenwald of the Guardian, who first broke the leaks, told the Daily Beast.
He added: "I don't know for sure whether he has more documents than the ones he has given me... I believe he does."
Do you believe the "doomsday cache" really exists?