WASHINGTON (NYTIMES, AFP)- The FBI secretly arrested a National Security Agency (NSA) contractor in recent weeks and is investigating whether he stole and disclosed highly classified computer codes developed to hack into the networks of foreign governments, according to several senior law enforcement and intelligence officials.

The theft raises the embarrassing prospect that for the second time in three years an insider has managed to steal highly damaging secret information from the NSA.

In 2013, Edward Snowden, who was also a contractor for the agency, took a vast trove of documents that were later passed to journalists, exposing NSA surveillance programmes in the United States and abroad.

The information believed stolen by this contractor - who like Snowden worked for the consulting firm Booz Allen Hamilton, which is responsible for building and operating many of the agency's most sensitive cyberoperations - appears to be different in nature from Snowden's theft.

The contractor arrested in recent weeks is suspected of taking the highly classified "source code" developed by the agency to break into computer systems of adversaries like Russia, China, Iran and North Korea.

Such access would enable the NSA to plant malware in rivals' systems and monitor - or even attack - their networks.

Two officials said that some of the information the contractor is suspected of taking was dated.

Booz Allen Hamilton and the NSA did not immediately respond to requests for comments.

The case first came to light in August, when mysterious hackers calling themselves the "Shadow Brokers" leaked online what appears to be classified NSA computer code.