New variants resurrect the malware four months after Microsoft and Kaspersky Lab took down the original, which was capable of sending nearly 4 billion spam e-mails each day.
The software giant and Andrey N. Sabelnikov, who admits he wrote the code used in malware that infected thousands of computers, reach a settlement in related lawsuit.
A Czech resident is accused of operating a botnet that infected tens of thousands of computers, serving spam and harvesting data. This is the third botnet Microsoft has taken down using the same legal and technical measures.
Researchers use specially crafted code to direct infected computers to their servers instead of servers run by the criminals who have been using the botnet to distribute spam.
St. Petersburg, Russia-based Andrey N. Sabelnikov says he is "absolutely not guilty" of participating in the creation of the huge spam network that Microsoft shut down last September.
Software giant accuses a St. Petersburg, Russia, resident of writing malware to control and nurture the botnet, which infected 41,000 computers worldwide.
Provider of free domains has agreed to delete or to transfer to Microsoft all subdomains the software giant had said were tied to the Kelihos botnet.
Botnet was responsible for 18 billion spam messages a day -- about 18 percent of the world's spam -- experts tell The New York Times.
At an event Wednesday morning in Washington, D.C., industry representatives will announce plans to fight back against botnets, which have become the Internet's leading security threat.
Discovery leads to investigation and disruption of Nitol botnet and attempt to shut down subdomains linked to more than 500 types of malware.