Starting in April 2006, Pho worked as a developer in the National Security Agency's Tailored Access Operations unit, which is involved in cyber operations.
The scope of harm in Pho's case is "not theoretical", said Gordon Johnson, special agent in charge of the FBI's Baltimore field office.
Former National Security Agency employee Nghia H. Pho, 67, of Maryland, pleaded guilty in US District Court for the District of Maryland to one count of willful retention of national defense information, according to charges unsealed on Friday through a US Department of Justice statement.
Pho is scheduled to be sentenced in April in US district court in Baltimore. Authorities found classified documents throughout his home, according to court documents, which Pho took from work between 2010 and 2015.
Nghia Hoang Pho, who worked in the NSA's elite hacking unit, retained U.S. government documents containing top-secret national defense information between 2010 and March 2015, the Justice Department said.
"This material was in both hard-copy and digital form, and was retained in Pho's residence in Maryland".
Pho is the same former NSA employee implicated in previous reports involving the Russian government and Kaspersky Lab, a Moscow-based antivirus vendor accused of being a conduit for the Putin administration's worldwide espionage efforts, both The Times and Reuters reported Friday.
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Pho had installed a popular antivirus software by Kaspersky Lab on his computer. Some US officials have said software from the Moscow-based company allowed Russian intelligence agencies to pilfer sensitive secrets from the United States through Pho's computer.
The alleged hack had been previously reported by the Times, The Wall Street Journal and others, but the employee's identity had not previously been revealed.
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.
Pho is the third former NSA employee to be charged by the agency in the past three years.
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.
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.
In June another NSA contractor, Reality Winner, 25, was charged with leaking classified material about Russian interference in the 2016 USA presidential election to a news outlet. He has pleaded not guilty.