Boston: Russian hackers exploited a bug in Microsoft Windows and other software to spy on computers used by NATO, the European Union, Ukraine and companies in the energy and telecommunications sectors, according to cyber intelligence firm iSight Partners.

ISight said it did not know what data had been found by the hackers, though it suspected they were seeking information on the Ukraine crisis, as well as diplomatic, energy and telecom issues, based on the targets and the contents of phishing emails used to infect computers with tainted files.

A Russian bug has been found targeting NATO computers. Credit:iStock

The five-year cyber espionage campaign is still going on, according to iSight, which dubbed the operation "Sandworm Team" because it found references to the Dune science fiction series in the software code used by the hackers.

The operation used a variety of ways to attack the targets over the years, iSight said, adding that the hackers began only in August to exploit a vulnerability found in most versions of Windows.