The internal watchdog reported a dozen instances in which the technology was abused and six of those cases were referred to the Justice Department for possible prosecution, CNN reported Friday.
In one instance, a civilian intelligence employee overseas allegedly used the NSA's signals intelligence collection system to listen to the phone conversations of nine foreign women between 1998 and 2003, the report said.
In another case, a civilian employee told NSA security she listened in on a foreign phone number in 2004 because she found the number in her husband's contacts and suspected him of being unfaithful. The woman resigned before she could be fired or demoted for her actions, the report said.
"I appreciate the transparency that the Inspector General has provided to the American people," said U.S. Sen. Chuck Grassley, R-Iowa, who requested a letter from the NSA detailing the infractions. "We shouldn't tolerate even one instance of misuse of this program. Robust oversight of the program must be completed to ensure that both national security and the Constitution are protected."
The NSA's phone tracking and email hacking has come under intense scrutiny since former security contractor Edward Snowden went public with details of the NSA's secret domestic spying programs.