WASHINGTON: A National Security Agency (NSA) contractor has been arrested and charged with stealing highly classified information, authorities said on Wednesday, a data breach that could mark a damaging new leak about the United States (US) government's surveillance efforts.

Harold Thomas Martin, 51, who worked for Booz Allen Hamilton, was taken into custody in Maryland in August, said a US official, speaking on condition of anonymity. Booze Allen is the consulting firm that employed Edward Snowden when he revealed the collection of metadata by the NSA in 2013.

Booz Allen said in a statement that when the company "learned of the arrest of one of its employees by the FBI," they immediately fired the employee and offered full cooperation to the Federal Bureau of Investigation (FBI).

The same month Martin was arrested, some of the NSA’s most sophisticated hacking tools were dumped onto public websites by a group calling itself Shadow Brokers.

The company’s stock was down 3.7 per cent to $30.33 a share, following the report.

The US Justice Department charged Martin, who had top secret national security clearance, with theft of classified government material, according to a criminal complaint unsealed on Wednesday.

Word of the arrest followed a New York Times report that the Federal Bureau of Investigation was investigating whether he stole and disclosed highly classified computer "source code" developed to hack into the networks of Russia, China, Iran, North Korea and other countries.

It was the latest disclosure of details of cyber spying by the U.S. government since Snowden stole and released a vast trove of documents that exposed the reach of the NSA's surveillance programs at home and abroad. It comes at a time of growing concern over the cyberhacking of federal agencies and American political parties.

According to the complaint, documents found in Martin's possession contained sensitive intelligence.

"These six documents were produced through sensitive government sources, methods, and capabilities, which are critical to a wide variety of national security issues," the complaint said. It said Martin had the ability to access US government property that was not permitted to leave its authorised location.

Martin's lawyer could not immediately be reached for comment.

The Justice Department's chief national security prosecutor, John Carlin, declined to comment on the specifics of the case.

He said, however, that insider threats have long posed a challenge to the government.

"I'm sure the trusted professionals I work with across the community will take a hard look at anything they can learn from this case, whether it's about contractors or other issues to see whether they can better defend our systems from others who might try to steal from them,” Carlin said in an interview on CSPAN.

Martin faces up to 10 years in prison if convicted on the most serious charges.

The leak of the NSA hacking tools coincided with US officials saying they had concluded that Russia or its proxies were responsible for hacking political party organisations in the run-up to the Nov 8 presidential election. The Russian government has denied involvement.