One of the most active threats we face today on the Internet is cyber-crime. Increasingly capable criminals are constantly developing more sophisticated means of profiting from online criminal activity. This paper demonstrates a growing, sophisticated technique called fast-flux service networks which we are seeing increasingly used in the wild. Fast-flux service networks are a network of compromised computer systems with public DNS records that are constantly changing, in some cases every few minutes. These constantly changing architectures make it much more difficult to track down criminal activities and shut down their operations.
In this paper we will first provide an overview of what fast-flux service networks are, how they operate, and how the criminal community is leveraging them, including two types which we have designated as single-flux and double-flux service networks. We then provide several examples of fast-flux service networks recently observed in the wild,. Next we detail how fast-flux service network malware operates and present the results of research where a honeypot was purposely infected with a fast-flux agent. Finally we cover how to detect, identify, and mitigate fast-flux service networks, primarily in large networking environments. At the end we supply five appendixes providing additional information for those interested in digging into more technical detail.