Microsoft and several of its partners have disrupted a number of cybercrime rings that used the Zeus malware to steal an estimated $100 million over the last five years.
The company said a consolidated legal case has been filed in the US against those allegedly responsible that for the first time applies the Racketeer Influenced and Corrupt Organisations (RICO) Act.
Zeus has been a thorn in the side for financial institutions due to its stealthy nature and advanced spying capabilities that center around stealing online banking and e-commerce credentials for fraud.
According to a complaint filed under seal on March 19 in the US District Court for the Eastern District of New York, Microsoft accused the defendants of infecting more than 13 million computers and stealing more than $100 million over the last five years.
The civil complaint lists 39 "John Doe" defendants, many of whom are identified only by online nicknames, such as "Gribodemon" and "Harderman."
It marks the latest action led by Microsoft against botnet operators. The company has gone to court before to gain permission to take control over domain names associated with the command-and-control infrastructure of botnets such as Kelihos, Rustock and Waledac.
The company has also initiated civil proceedings against unnamed operators but has had little success due to jurisdiction issues.
Mark Debenham, senior manager of investigations for Microsoft's Digital Crimes Unit, said the creators of Zeus - as well as related malware such as SpyEye and Ice-IX - sold "builder kits" to other would-be cybercriminals. Simple versions sold for as little as $700, while more advanced versions could cost $15,000 or more, according to Debenham's affidavit.
Microsoft also said this is the first time other parties have joined it as a plaintiff in a botnet case. The other plaintiffs are the Financial Services Information Sharing and Analysis Center, a nonprofit security organisation, and the National Automated Clearing House Association (NACHA).
NACHA oversees the Automated Clearing House system (ACH), a widely-used but aging system used by financial institutions for exchanging details of direct deposits, checks and cash transfers made by businesses and individuals. It has been heavily targeted by Zeus.
In a single day in August 2011, 167 million phishing emails purported to be from NACHA were sent, according to a sworn affidavit included in the court documents from Pamela Moore, senior vice president of administrative services and NACHA's CFO. Those emails tried to entice victims into clicking links that led to malicious servers which would then install Zeus, she testified.
Domains and servers seized
On a normal day, NACHA would only send out about 1,500 legitimate messages.
"The Zeus botnets have caused, and continue to cause, extreme damage to NACHA and its members, which, if allowed to continue, will be compounded as the case proceeds," Moore testified.
The court granted Microsoft and its partners permission to seize servers located in Scranton, Pennsylvania, and Lombard, Illinois, on Friday. Microsoft has also taken control of 800 domains that are part of Zeus' infrastructure in an attempt to completely wrest control of the networks from their operators.
Microsoft said the action resulted in the disruption of several of Zeus botnets, and it would now work to identify and notify people whose computers are infected with the malicious software. Also contributing to the action was Finnish security vendor F-Secure and Kyrus Tech, a security company.