The personal computer used by the National Security Agency (NSA) employee who reportedly took classified tools from the office and loaded them onto that home machine was infected with a backdoor associated with Russian underground forums. Another 120 pieces of malware were flagged on the machine.

That's the latest finding of an internal investigation published today by Kaspersky Lab, which has been under scrutiny amid allegations that its software assisted Russian nation-state actors in stealing the NSA hacking tools off the employee's home computer, which was running Kaspersky Lab antivirus software. The security company has vigorously denied the allegations.

According to the security firm's investigation, the NSA employee's PC was infected with the Mokes backdoor, aka Smoke Bot and Smoke Loader. The information-stealing backdoor Trojan has been for sale since 2014 in Russian cybercrime underground forums, and from September to November 2011, its command-and-control servers were "registered to presumably a Chinese entity going by the name “Zhou Lou”," Kaspersky Lab's report says.

The NSA worker's machine was breached on Oct. 4, 2014, after he installed what appeared to be a pirated Office 2013 application, and Kaspersky Lab's AV later detected the malware as Mokes.

"At a later time after installation of the supposed MS Office 2013, the antivirus began blocking connections out on a regular basis to the URL “http://xvidmovies[.]in/dir/index.php”. Looking into this domain, we can quickly find other malicious files that beacon to the same URL. It's important to note that the reason we know the system was beaconing to this URL is because we were actively blocking it as it was a known bad site. This does however indicate the user actively downloaded / installed malware on the same system around the same time frame as our detections on the Equation files," Kaspersky Lab said in its report.

To have installed and run the malware in the first place, the victim would have had to disable Kaspersky Lab's AV program, the company said.

During the period of September 11 and November 17, 2014, some 121 pieces of malware including Mokes and not including the NSA tools, were flagged by Kaspersky Lab's software. The malware included other backdoors, Trojans, adware, and exploits. "All of these alerts, combined with the limited amount of available telemetry, means that while we can confirm our product spotted the threats, it is impossible to determine if they were executing during the period the product was disabled," the report says.

The AV operated normally when it flagged the tools created by the Equation Group, Kaspersky Lab says. Equation Group is the moniker the security firm uses for the NSA since it steers clear of attribution of actual attack groups.

"In no way was the software used outside of this scope to either pull back additional files that did not fire on a malware signature or were not part of the archive that fired on these signatures," the report says. "What is believed to be potentially classified information was pulled back because it was contained within an archive that fired on an Equation specific malware signatures."

The security firm said it found no evidence that its researchers attempted to set up rogue signatures to search for classified or top-secret files on the NSA worker's machine.

Given the discovery of the Mokes backdoor infection and possible infections from other malware on the machine, Kaspersky Lab concluded that the data "could have been leaked to an unknown number of third-parties as a result of remote access to the computer." 

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