Microsoft says it has discovered the mastermind behind a botnet that infected computers with viruses that take control of computers and use them to spam others with Microsoft Hotmail and Outlook email.

In a complaint (pdf, 21 pages) filed Monday in federal court in Virginia, Microsoft said Russian citizen Andrey N. Sabelnikov wrote the code for and either created, or participated in creating, the Kelihos malware.

In the civil complaint, Microsoft says Sabelnikov lives in St. Petersburg and is a software engineer and project manager at a company that provided firewall, antivirus and security software. He has a degree from the Department of Computer Systems and Programming, St. Petersburg State University of Aerospace Instrument Engineering, according to Microsoft's complaint.

In September, Microsoft said it took down a botnet called Kelihos in an operation code-named “Operation b79.”

Microsoft, in a complaint in federal court related to the botnet, named Dominique Alexander Piatti, dotFREE Group SRO and John Does 1-22 as the owners of a domain used to register other subdomains to operate the Kelihos botnet.

Microsoft later reached a settlement and dropped its lawsuit against Piatti, after determining the business owner was not directly involved with infecting internet users’ computers and using them to send billions of spam messages and steal personal information of people with Hotmail accounts.

Microsoft says that Sabelnikov “registered more than 3,700 ‘cz.cc’ subdomains from Piatti and dotFREE Group SRO, and misused those subdomains to operate and control the Kelihos botnet.”

Sabelnikov has not yet responded to the complaint. He could not be reached for comment.