Washington (CNN) A hacker penetrated an Air Force captain's computer to steal sensitive information about US military drones, according to new research by cybersecurity investigators at Recorded Future, a threat intelligence firm.

The documents, while not classified, include a private list of airmen working with MQ-9A Reaper drones and maintenance and course material on the weapons - the US-made deadly unmanned aerial vehicle used around the world to surveille and strike targets.

US law enforcement is investigating the breach, according to Recorded Future's Insikt Group, which conducted the research. The firm said its researchers have a "high degree of confidence" the hacker is from South America, though it did not elaborate further, citing the ongoing investigation.

"The FBI does not confirm or deny the existence of investigations," Lauren Hagee, an FBI spokeswoman, said in an email to CNN. The Air Force did not immediately respond to requests for comment.

The attack is the latest in a long line of breaches in military and other public sector domains, including a recent hack of a Navy contractor that exposed a large amount of sensitive data on submarines and undersea weaponry, according to the Washington Post. US officials pointed the finger at China for that theft.

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