Russian hackers stole National Security Agency cyber secrets after a contractor placed highly classified data on a home computer. The sensitive data included details on preventing cyber-attacks and exploiting foreign computer networks. The theft is likely to rank as one of the most important breaches in security, Reuters reported. The NSA-contracted employee was using Kaspersky antivirus software, according to the Washington Post.

While the National Security Agency (NSA) has declined comment about the significant security breach, federal prosecutors continue to investigate the 2015 case.

The employee took sensitive material home to work on it there, and along with running the Russian-backed antivirus software on his computer, enabled hackers to have access to his files, the Post noted.

Elite NSA hacker’s computer conduit for cyber theft by Russia

The worker was employed at Tailored Access Operations, which is an elite unit of NSA’s hacking division that creates tools for penetrating computers in order to obtain foreign intelligence. Though the employee was fired in 2015, he reportedly did not take the materials home with malicious intent – such as passing the classified data to a foreign counterintelligence agency, according to the Post.

As a result of the NSA material being stolen, the Russian government was, in turn, able to more readily detect and avoid cyber spying operations, track activities, and thwart defensive steps by the United States government.

The 2015 case, is the more recent harmful NSA breach and fuels the U.S. intelligence community’s belief that Kaspersky Lab’s software functions as a means for espionage by Russia.

Senator sounds alarm about public, government using Russian software

Democratic Senator Jeanne Shaheen (NH) is an outspoken critic of Kaspersky’s software and has advocated for a ban on the software’s use in federal computer networks.

She has asserted that there are “serious dangers” of the public and local, state, and federal governments using the company’s software, the Post reported. The NSA intrusion, she said, is a “stark warning.”

Among the material the employee had taken home to work on was hacking tools. He was assisting in developing tools aimed as replacements for tools believed to have been compromised after the NSA breach of material, as well, by Edward Snowden, a former contractor.

The Post stated that the 2015 NSA security intrusion highlights the security risks entailed in using software that is as seemingly innocuous as virus detection applications.

U.S. intelligence community says Kaspersky Lab linked to Russia

The intelligence community in the United States has reportedly long-held the belief that Kaspersky is linked to the Russian government. Kaspersky Lab asserts that it is not inappropriately tied to the government in Russia, however. The company further stated that news continuing to “perpetuate accusations about the company” is unfortunate” according to the Post. Kaspersky Lab claims it has not received evidence to substantiate unproven claims.

Last month, the Department of Homeland Security (DHS) gave civilian agencies, on DHS networks, 90 days to identify and remove Kaspersky software, unless the agencies were directed otherwise.

DHS said the order was given because the company has ties to the Russian government and the software does present a security risk, the Post wrote.

Nebraska Senator says can’t beat opponent by handing over ‘playbook’

Republican Senator Ben Sasse (NE) said that it is more difficult “to beat your opponent when they’re reading your playbook,” according to the Post. He also stated that it is “even worse when someone on your team gives it to them.” He said the United States can’t afford “self-inflicted injuries” since Russia is clearly a United States adversary in cyberspace.