More than two months after documents leaked by former contractor Edward Snowden first began appearing in the news media, the National Security Agency still doesn’t know the full extent of what he took, according to intelligence community sources, and is “overwhelmed” trying to assess the damage.

Officials, including NSA Director Keith Alexander, have assured the public that the government knows the scope of the damage, but two separate sources briefed on the matter told NBC News that the NSA has been unable to determine how many documents he took and what they are.

Sources said authorities believe the trove of unreleased materials includes details of data collection by U.S. allies, including the U.K., Canada, Australia and New Zealand. These English-speaking allies, known along with the U.S. as the “Five Eyes,” are critical to U.S. intelligence efforts.