Ukrainian police on Tuesday seized the servers of an accounting software firm suspected of spreading a malware virus that crippled computer systems at major companies around the world last week, a senior police official said.

The head of Ukraine¡¯s Cyber Police, Serhiy Demedyuk, told Reuters the servers of M.E.Doc ¡ª Ukraine¡¯s most popular accounting software ¡ª had been seized as part of an investigation into the attack.

Though they are still trying to establish who was behind last week¡¯s attack, Ukrainian intelligence officials and security firms have said some of the initial infections were spread via a malicious update issued by M.E.Doc, charges the company¡¯s owners deny.