When a coalition of companies used sinkhole servers to wrest control of and shut down the Kelihos.B botnet, it took less than a day for the botnet to be replaced by a strikingly similar malware network. Security firms debated whether the botnet had escaped destruction, but in the end the takedown appeared to do little more than inconvenience the operators.
In a recent series of blog posts, Brian Foster, chief technology officer of network security vendor Damballa, criticized the companies that have endeavored to shut down botnets for missing their collective marks. Foster called out takedown efforts for being haphazard, missing secondary communication methods, and failing to lead to the arrest of the operator.
"If security researchers and their organizations are doing takedowns for marketing reasons, then it doesn't matter how they go about it," he wrote. "But if they are doing takedowns to truly limit Internet abuse and protect end users, then there needs to be a more thoughtful approach than what has typically been used by the industry."
In a follow-up interview, Foster stressed that takedowns can be done right, but need to be done in a more systematic manner that catches backup communication channels, speeds takedowns, and allows for the gathering of evidence that can be used against the operators.
Yet companies that have done botnet takedowns counter that the approach has indeed been effective. Microsoft, for example, has disrupted seven botnets, using civil complaints to allow it to seize servers and gather evidence on the botnets and their operators. In its latest takedown, Microsoft partnered with financial firms and law enforcement agencies worldwide to disrupt the Citadel botnet, which the company claims has infected 5 million systems and caused more than a half-billion dollars in damages. While the botnet may be resurrected by its operators, the effort has still had a net positive effect, argues Richard Boscovich, assistant general counsel of Microsoft's Digital Crimes Unit.
"If you look at the benefits of the takedown in a very specific way -- whether the number of botnets has gone down -- then you could say the jury is still out," he says. "But that is not a complete, nor holistic, way of looking at the actions."
The number of people whose systems have been cleaned by industry, academic, and government partners is a large benefit. The increase in public awareness is another great benefit, he says. And the partnerships established between researchers, industry, and law enforcement will serve the industry well in the future. "How can you argue that there is no value in that?" he says.
[Botnet hunters debate whether Kelihos/Hlux operators can reclaim rescued bots. See It's (Already) Baaack: Kelihos Botnet Rebounds With New Variant.]
Security firm FireEye, which has participated in five botnet takedowns, points to the continued reduction in spam following the shutdown of McColo as an indication that the strategy can succeed. The California-based Internet service provider hosted the command-and-control networks for a number of botnets and was shut down in 2008, leading to a permanent decrease in spam.
"These botnets are no longer sending any spam at all, and that shows the success of the botnet takedown," says Atif Mushtaf, senior staff scientist with FireEye.
Industry efforts to take down botnets have always been controversial. In many ways, botnet takedowns are a result of the high level of frustration with the seemingly endless attacks on the networks and computer systems of businesses, governments, and individuals. Yet, in pursuing takedowns, companies and researchers need to analyze the impact of their actions to make sure they are not crossing ethical lines, David Dittrich, an information security engineer at the University of Washington, told attendees at the North American Network Operators Group conference in October.
"You need to be capable of justifying what it is that you are doing because what you are doing might be illegal -- in your country or in the country where the computer is that you are dealing with," Dittrich said during his talk. "And you should try to go through this in a progressive way, working as much as you can toward cooperation, reporting to people and making sure that they are doing their thing, and not just jumping to strike back or counterstrike."
Researchers and companies need to come up with better definitions to describe botnets and associated malware and infrastructure, and a more scientific way of counting them to avoid confusion and inflated estimates of botnet size. Taking a more measured approach to botnet takedowns can help head off criticisms of grandstanding, he says.
In addition, companies need to work better with other researchers and find ways to scale the efforts so that more companies, and not just technology firms, can lead takedown efforts, says Microsoft's Boscovich.
"You have to scale," he say. "We should not be the only companies doing this or leading this. There has to be more people out there doing more of these."
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