U.S. intelligence officials suspect that Edward Snowden's exposure of classified materials is probably the largest in American history, but they may never know its full extent because of how he skillfully hid his tracks, The New York Times reported.
Snowden has been indicted for espionage. The harm he has done to U.S. security and political interests has been variously described by authorities as "irreversible," "incalculable" and "potentially catastrophic."
Despite hundreds of hours aimed at reconstructing the scope of Snowden's breach, officials say they do not know— and are unlikely to ever uncover— "all of what he took," according to the Times.
One guesstimate is that he stole 1.7 million documents including super-secret files that would be released by supporters if something happened to him.
Snowden, now living under asylum in Russia, took months to amass the data. He took advantage of his location as an N.S.A. contractor in Hawaii, where the facilities were not equipped with software that would allow authorities to retrace his activities.
The N.S.A. says that Snowden's access was the same as anyone else's with a high-level security clearance. It would have been routine for him to transfer large amounts of data from point to point within the system.
Snowden used the passwords of colleagues and, exploiting his knowledge of system architecture, hacked into firewalls allowing him an unknown degree of navigational access.
He announced that he handed over all of the purloined materials to sympathetic journalists, though authorities are not convinced that he hasn't held on to some of the data.
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