Officials Say US May Never Know Extent of Snowden’s Leaks

American intelligence and law enforcement investigators have concluded that they may never know the entirety of what the former National Security Agency contractor Edward J. Snowden extracted from classified government computers before leaving the United States, according to senior government officials.

Investigators remain in the dark about the extent of the data breach partly because the NSA facility in Hawaii where Snowden worked -- unlike other NSA facilities -- was not equipped with up-to-date software that allows the spy agency to monitor which corners of its vast computer landscape its employees are navigating at any given time. Six months since the investigation began, officials said Mr. Snowden had further covered his tracks by logging into classified systems using the passwords of other security agency employees, as well as by hacking firewalls installed to limit access to certain parts of the system.