Posted by Virus Bulletin on Feb 22, 2012
Increasing use of UDP to avoid communication tracking.
Researchers at Symantec have discovered a new parallel build of Zeus (also known as Zbot) and SpyEye that appears to be entirely controlled through peer-to-peer communication.
Most botnets are controlled through a number of command-and-control servers, that are used to control the behaviour of the thousands of bots under the botherder's command. From the botherder's point of view, the downside to this set-up is that the botnet can effectively be taken down by shutting down these command-and-control servers, the location of which can also help to trace the botherder. There are also sites such as Zeustracker that track the IP addresses of these servers, allowing for security software to block traffic to and from them.
A previous version of Zeus already used peer-to-peer (P2P) for communication within the botnet, but still depended on central command and control servers. The new version appears to do away with them altogether. As each node in the botnet is now of equal importance, even if it were possible to take down such nodes (most of which are home PCs), it would not stop the botnet from operating.
The use of P2P is not the only improvement in the new build. Most data exchange within the botnet now happens over UDP rather than TCP. Unlike TCP, UDP is a stateless protocol, making it more difficult to extract and capture data from communications within the botnet.
Another change is that each bot now acts as an HTTP server which, among other things, is used to serve malware - in this particular case fake anti-virus and a proxy engine.
Finally, the researchers remark that the lack of a central server might make it hard for the botherders to extract stolen data from the botnet. They are still analysing the samples and have not excluded the possibility that for such purposes the botnet does make use of some kind of command-and-control server.