Microsoft is continuing its legal tear against botnets: It has now named the botnet operator of the Kelihos botnet that it helped take down last fall.

The alleged perpetrator, Andrey N. Sabelnikov, a Russian engineer, has been added to Microsoft’s legal suit filed in U.S. District Court in September in relation to the botnet. The company, which worked with Kaspersky Lab and Kyrus to take down the spamming botnet, says the initial claim named co-defendants Dominique Alexander Piatti and dotFREE Group SRO in Microsoft’s civil lawsuit cooperated and provided information that led to the latest legal action against Sabelnikov as part of a settlement in October.

“In today’s complaint, Microsoft presented evidence to the court that Mr. 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 analyzing the Kelihos malware,” said Richard Domingues Boscovich, senior attorney for Microsoft’s Digital Crimes Unit. “Microsoft also alleges that Mr. Sabelnikov registered more than 3,700 ‘cz.cc’ subdomains from Mr. Piatti and dotFREE Group SRO, and misused those subdomains to operate and control the Kelihos botnet.”

Microsoft says Sabelnikov lives in St. Petersburg, Russia, and is a contractor for a software development and consulting firm who once worked as a software engineer and project manager at a firewall and antivirus firm. According to KrebsOnSecurity, that firm was Agnitum.

The Kelihos botnet was a relatively small one of some 41,000 infected bots, but was used to spam, steal financial information, and wage distributed denial-of-service attacks; it was capable of sending 3.8 billion spam e-mails per day. It’s now inactive, but Microsoft says there are still thousands of computers infected with its bot malware.

Meanwhile, Microsoft’s initial lawsuit alleged that Piatti, dotFREE Group SRO, and John Does 1-22 owned and used the “cz.cc” domain to register other subdomains used in Kelihos.

“Our investigation showed that while some of the defendants’ subdomains may have been legitimate, many were being used for questionable purposes with links to a variety of disreputable online activities. On Oct. 26, we successfully settled with defendants Dominique Alexander Piatti and dotFREE Group, allowing us to dismiss the case against them. Today, thanks to their cooperation and new evidence, we have named a new defendant to the civil lawsuit we believe to be the operator of the Kelihos botnet,” Boscovich said.

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