A botnet, a network of unwillingly controlled computers, is sometimes called a Zombie network. That’s because, like “real zombies” the computer owners aren’t aware of what has happened to them. In the case of the Kelihos botnet, a better term might be a Vampire network.
The network has been “killed” several times, but always manages to rise from the dead! Like Vampires of lore, Kelhios is a predator that attacks computer users, usually for schemes related to financial fraud.
When first discovered in December 2010, the Kelihos botnet consisted of at least 45,000 computers that were be used to spew email spam and conduct Denial of Service attacks. While the number of computers in the network was particularly large, there have been botnets in the millions; Kelihos was capable of generating up to 3 billion spam messages per day.
In September 2012, Microsoft announced that they had been able to pull the plug on Kelihos. This was no small feat. Unlike other botnets, Kelihos is a pear to pear network with no command and control servers. In the case of Waledac botnet, Microsoft was able to get a court order to seize the networks servers.
Bringing down Kelihos involved shutting down all of the domains that were spreading the malware that infected computers and made them part of the network., plus “infecting” the zombie computers with a reverse engineered version of the malware that seizes control of the computer from the Kelihos operators. The process is known as “sinkholing”, where the bots are disconnected from the botnet and controlled by friendly computers.
It was a unique and dramatic success, but the story does not end there.
An even larger botnet, estimated at 110,000, computers was discovered in January 2012 that was based on the same code as Kelihos, also known as Version 2. There were not the same controlled computers, but it was a slightly modified version of the controlling software. The ability to steal bitcoins was added for the first time to the network. A bitcoin is a digital currency that can be exchanged for real money.
A key change in version 2 was the ability to spread via removable drives such as USB sticks. It was also determined that the malware was being spread from domains in Russia instead of Europe, making it more difficult to diagnose and shut down.
The second version of the botnet itself was shut down by it in March 2012 by several privately owned firms who used the same approach pioneered by Microsoft. Evidently, it was far from a silver stake through Kelihos’s heart. Evidence of a reappearance of the botnet first was reporting the next month.
It was not until February 2013 that the third iteration of Kelihos became widely known. However, according the security firm CrowdStrike Version 3 of Kelihos was being implemented within 20 minutes of the Version 2 takedown. The Kelihos operators apparently had contingency plans with software improvements already in place to get the botnet back up and make it more difficult to take down in the future.
In one of the more dramatic events in Internet Security history, CrowdStrike conducted a live takedown of Kelihos Version 3 at the February 2013 RSA convention on Internet Security. The convention audience could watch a global map as thousands of Kelihos bots went from being in the botnet to being sinkholed and controlled by friendlies.
CrowdStrike had determined that bots regularly “checked in” to proxy servers and were updated with a list of what, to them, were friendly bots in the network that they could connect to. CrowdStrike’s new method of sinkholing involves spreading a substitute list of computers that take the bots offline when connected to.
Brilliant and a real crowd pleaser at the RSA Convention. But is Kelihos really dead? It doesn’t appear to be. Recent reports indicate that it is very much alive. There is way too much money in the spam and financial fraud that such a botnet can commit to expect the creators to go quietly into the good night. New botnets are being reported on a regular basis and the peer-to-peer design pioneered by Kelihos has become popular botnet creators.
What should I do about botnets?
And you need to be vigilant. When you visit a web site, check for an EV SSL certificate before ever downloading software or providing personal information. If you are protecting a network, in addition to the obvious the best advice is to simply not give most users admin rights to install software. Users hate that restriction, I know I do. It is the best way, however, to ensure a drive by download can’t kick off and install malware before the virus scanner can catch it.