Embattled security vendor Kaspersky Labs has released a report based on the telemetry data its antivirus collected from a computer used by an NSA employee, claiming the system contained large amounts of malware.
The report said the information Kaspersky obtained showed the NSA staffer's home computer had been infected by malware that acted as a backdoor to the computer.
This backdoor could have been used to leak classified documents and hacking tools belonging to the NSA.
The NSA employee worked for the Tailored Access Operations (TAO) group of hackers at the agency.
Media reports have suggested Kaspersky siphoned off the secret NSA files with its software, and passed them onto the Russian government.
While it acknowledged that its antivirus detected and collected the NSA hacking tools as part of its normal functionality, the security vendor has strenuously denied allegations it gave them to Russia.
Kaspersky said the computer had more than 120 other types of malware on it including a second backdoor, but the company said this did not appear to have communicated with a command and control server.
The security vendor noted that the NSA employee had tried to run what appeared to be a pirated version of Microsoft Office that contained malware.
It said the staffer must have disabled the Kaspersky antivirus to do so.
"Executing the malware would not have been possible with the antivirus enabled," it said.
Hacking tools leaked from the NSA have found their way into malware used in large-scale attacks around the world.
Kaspersky is under fire in the United States for allegedly supplying information to the Russian government. The US government has banned agencies from using the security vendor's products.