Cyber intelligence firm iSight Partners reported that a group of Russian hackers connected to the government exploited a bug in Microsoft Windows to spy on computers used by NATO, Ukraine and private companies. The researchers believe that the hackers might be planning to manipulate files related to the Ukraine crisis.

The operation dubbed as "Sandworm Team" has been operational for five years, but the hackers targeted Windows just two months ago. iSight immediately alerted Microsoft regarding this vulnerability and some of the victims. The firm will also release a 16-page report regarding the attack on Tuesday, according to Reuters.

Microsoft, on the other hand, said that it will release an update to fix the bug on Tuesday.

The security firm presumed that the hackers are Russian, specifically working for the Russian government, because of the language used and the files stored in an unprotected server. The operation is also related to espionage instead of cybercrime, the firm said.

"We cannot say with 100 percent certainty we're talking about some guy in the Russian government building," iSight spokesman Stephen Ward told the Wall Street Journal. "But we can say this is cyberespionage, and it's cyberespionage focused on Russian objectives."

The hackers reportedly targeted the computers of Ukrainian officials using the latest versions of Windows software. The bug was able to get into the system through PowerPoint documents sent through emails containing false intelligence reports from Russian supporters. The program is activated as soon as the file is opened.

"It's possible they've become more active in response to the Ukrainian situation," an former intelligence official told the Washington Post. "And when you become more active, you increase your likelihood of getting caught."

The Russian government, NATO, the European Union and the Ukraine government have not responded yet to this issue. But it is most likely that the Russian government will deny such allegations like it did in the past.