A former information security engineer had operated the Kelihos botnet, the primary distribution system for the MacDefender malware, Microsoft says.
Microsoft alleged Andrey Sabelnikov, a Russian citizen and former security vendor staffer, was responsible operations of the botnet.
The Redmond giant took down Kelihos in September.
Microsoft Digital Crimes Unit senior attorney Richard Boscovich said it presented to court evidence that Sabelnikov wrote the code for and either created, or participated in creating, the Kelihos malware.
“Further, the complaint alleges that he used the malware to control, operate, maintain and grow the Kelihos botnet. These allegations are based on evidence Microsoft investigators uncovered while analysing the Kelihos malware," Boscovich said.
Microsoft alleged Sabelnikov registered more than 3,700 cz.cc subdomains from Dominique Alexander Piatti and dotFREE Group SRO, and used them to operate Kelihos.
Charges against against Alexander PiattiPiatti and dotFREE Group were settled and dismissed last year.
It was also revealed that Sabelnikov worked as a software engineer and project manager at Russian anti-virus firm Agnitum, a provider of firewalls, anti-virus and security software.
Microsoft doesn't specify where Sabelnikov worked, but security blogger Brian Krebs pointed out that Sabelnikov's LinkedIn page said he worked at the company from 2005 to 2007.
Krebs said that Sabelnikov's alleged role was discovered after a security researcher obtained a copy of the source code to Kelihos, who noticed it contained debug code that downloaded a Kelihos malware installer from the domain sabelnikov.net, a photography site registered to Sabelnikov's name.
That site currently links to Sabelnikov's profile page at Russian social networking site Vkontakte.ru, which includes the same pictures found in the LinkedIn profile.
Despite the takedown, Boscovich said that thousands of computers remain infected and that the case "is not over".