The guilty plea said that between 2010 and March 2015, Pho removed and retained at his home paper and digital copies of USA government documents and writings containing national defense information.
Pho was nabbed because he used Kaspersky Lab anti-virus software, which is banned on federal government computers out of fear that it could enable Russian government spying - Kaspersky is a Russian firm.
On Friday, the 67-year-old Nghia Hoang Pho pleaded guilty to removing the top-secret data and storing it in his Maryland home.
Pho is the third person working for the NSA to be arrested for removing classified information since October of a year ago - with contractor Reality Winner and NSA employee Harold Martin III preceding him. Pho now awaits sentencing for his crime, which can carry up to 10 years in prison, though prosecutors agreed not to seek more than eight years.
Pho had worked on highly classified projects and was employed from 2006 as a Tailored Access Operations (TAO) developer for the NSA, the news release said. U.S. officials have said the firm either has ties to Russian intelligence or is forced to share information held on its servers with Russian officials.
Pho, who was born in Vietnam and is a naturalized USA citizen, is free pending his sentencing, which is set for April 6, Bonsib said. But the nature of the threat was not fully realized until it was discovered Pho had installed a popular antivirus software by Kaspersky Lab, a software company based in Russian Federation, which is believed to have been exploited to steal the files from Pho's computer.
A former employee for the NSA who worked to infiltrate foreign computer networks has admitted to illegally taking classified documents from the agency.
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Asked for comment, Pho's attorney, Robert Bonsib, said, "Any conversations regarding this case will be made in the courtroom during the sentencing".
The National Security Agency headquarters building in Fort Meade, Maryland.
Kaspersky executives have repeatedly denied allegations that the company is working with Russian intelligence.
And Harold T. Martin III was arrested in 2016 after Federal Bureau of Investigation agents discovered some 50 terabytes of data and documents that Martin had taken from the NSA and other agencies over a period of 20 years.
The charges come on the heels of another government investigation in relation to a larger breach of NSA security, in which the NSA's hacking tools were released to the public previous year by an unidentified group called the Shadow Brokers, Wired reported.
Reality Leigh Winner, a Texas native who had been stationed in Maryland, was charged in June with sending a classified report to a news organization. Martin was indicted in February on charges of violating the Espionage Act.