As the Net Churns: Fast-Flux Botnet Observations
Jose Nazario, Thorsten Holz
International Conference on Malicious and Unwanted Software, October 2008
While botnets themselves provide a rich platform for financial gain for the botnet master, the use of the infected hosts as webservers can provide an additional botnet use. Botnet herders often use fast-flux DNS techniques to host unwanted or illegal content within a botnet. These techniques change the mapping of the domain name to different bots within the botnet with constant shifting, while the bots simply relay content back to a central server. This can give the attackers additional stepping stones to thwart takedown and can obscure their true origins.
Evidence suggests that more attackers are adopting fastflux techniques, but very little data has been gathered to discover what these botnets are being used for. To address this gap in understanding, we have been mining live traffic to discover new fast-flux domains and then tracking those botnets with active measurements for several months. We have identified over 900 fast-flux domain names from early to mid 2008 and monitored their use across the Internet to discern fast-flux botnet behaviors. We found that the active lifetimes of fast-flux botnets vary from less than one day to months, domains that are used in fast-flux operations are often registered but dormant for months prior to activation, that these botnets are associated with a broad range of online fraud and crime including pharmacy sites, phishing and malware distribution, and that we can identify distinct botnets across multiple domain names. We support our findings through an in-depth examination of an Internet-scale data continuously collected for hundreds of domain names over several months.[pdf]