An apparently unsuspecting employee of the U.S. National Security Agency handed over an encrypted digital key to whistleblower Edward Snowden, thus enabling the former contractor to the NSA to gain access to vast troves of classified materials, according to an NSA memo sent to Congress.

The Associated Press reported that this unnamed employee then resigned from the agency last month after the government revoked his security clearance, as outlined in a letter written by NSA Legislative Director Ethan Bauman to the House of Representatives’ Judiciary Committee.

In addition to this person, a military employee and a private contractor were also said to have been denied access to NSA data as part of the continuing investigation by the Federal Bureau of Investigation, Mr. Bauman said.

Mr. Snowden’s exposés last summer, on the NSA’s mass global surveillance of Internet and telephone communications, led to heightened pressure on the Obama administration in the Congress and anger expressed by leaders of other nations such as Brazil and Germany, amidst calls to rein in the spying programmes.

Although Mr. Snowden, who won temporary asylum in Russia after fleeing the U.S., has denied that he stole computer passwords or tricked some co-workers into giving him their passwords, the NSA letter was said to suggest that he “tricked at least one co-worker and copied the employee’s password without his knowledge.”

Specifically the civilian NSA worker in question reportedly told FBI investigators that he “allowed Snowden to use an encrypted digital key known as a Public Key Infrastructure certificate to gain access to classified information on NSANet, the agency’s computer network,” and this gave Mr. Snowden access to classified NSA databanks that he would otherwise not have had.

However Mr. Bauman was said to have told Congressmen that the civilian NSA employee “was not aware that Mr. Snowden intended to reveal any classified information,” and it remained unclear as to how much classified information Mr. Snowden had collected before using the co-worker’s password.

Reports said that in November the NSA suspended the civilian worker’s security clearance and then informed the employee it planned to fire him. He apparently resigned in January, according to Mr. Bauman.

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