Russian hackers have targeted NATO computers and the Ukrainian government, a cyber-intelligence firm said on Tuesday.

iSight Partners, one of the world’s leading companies in cyber threat intelligence, said that “many of the attempted hacks observed have been specific to the Ukrainian conflict and to broader geopolitical issues related to Russia.”

The firm explained that hackers have used what is known as a 'zero-day vulnerability.'

This is an attack which exploits a previously unknown weakness in all supported versions of Microsoft Windows and Windows Servers 2008 and 2012. Windows XP, however, is impervious to this form of attack.

Hackers also appear to have targeted the computers of energy sector firms, especially in Poland, as well as European telecommunications companies and academic organizations in the United States.

iSight Partners have said that they are tracking active campaigns by at least five distinct groups of hackers.

“It is critical to note that visibility is limited and that there is a potential for broader targeting from these groups (and potentially from other threats),” the firm said. 

None of the affected institutions have commented on iSight Partners claims as of yet.

The firm unveiled that they had been monitoring the activities of one of these groups -- dubbed as the 'Sandworm Team' -- since late 2013.

In late August, while tracking the group, iSight discovered a spear phishing campaign targeting the Ukrainian government and at least one organization in the United States.

“Notably, these spear phishing attacks coincided with the NATO summit on Ukraine held in Wales,” the company said.

Spear fishing is when a fraudulent e-mail attempts to target a specific organization, seeking unauthorized access to confidential data.

Last February, former Ukrainian President Victor Yanukovych refused to sign an EU association agreement following pressure from Russia.

He was subsequently overthrown in a popular uprising, which has led to increased tensions between Kiev and Moscow.

Thousands of people have been killed in fighting between the Ukrainian army and pro-Russian separatists in the eastern part of the country, home to many Russian-speaking Ukrainians, since Kiev’s anti-terrorist operations began.  

Anadolu Agency