WASHINGTON (REUTERS) - Microsoft said in a blog post on Saturday (Jan 15) that it observed destructive malware in systems belonging to several Ukrainian government agencies and organisations that work closely with the government.

The victims of the malware include Ukrainian government agencies that provide critical executive branch or emergency response functions, Microsoft said.

Also affected was an information technology firm that manages websites for public- and private-sector clients, including government agencies whose websites were recently defaced. Microsoft did not identify the information technology firm involved.

The United States software giant, which first detected the malware on Thursday, said the malware attacks did not make use of any vulnerability in Microsoft products and services.

A massive cyber attack hit government websites on Thursday night, warning Ukrainians to "be afraid and expect the worst". It left some websites inaccessible on Friday morning and prompted Ukraine to open an investigation.

Reuters reported on Saturday that Ukraine suspected a hacker group linked to Belarus intelligence had carried out the cyber attack, and that it used malware similar to that used by a group tied to Russian intelligence.

The malware, which is disguised as ransomware, would render the infected computer system inoperable if activated by the attacker, Microsoft said, adding that the company will continue to work with the cyber-security community to identify and assist targets and victims.