This is a summary of a paper, titled Your Botnet is My Botnet: Analysis of a Botnet Takeover.
Botnets are becoming a large problem for the internet. They are formed by networks of compromised computers that are under the control of some other person. Botnets are becoming the primary means for criminals to launch DOS attacks, steal personal data, or other cyber crimes.
Most previous analysis of botnets have been analyzing them from the inside; intentionally infecting a computer to join the botnet, and analyzing the activity that then occurs. Since many botnets use P2P protocols, other infected computers can be discovered using this technique. However, this gives a very limited view of the activities of the botnet. A better way is to take control of the entire botnet, which can be done either with cooperation from domain registrars or law enforcement.
For this paper, researchers took control of the Torpig botnet. Torpig is primarily associated with bank account and credit card theft. This was done by exploiting how the bots try to locate their command server. Each bot generates a list of domains to contact, and the first host that sends a reply identifying itself is considered genuine until the next domain generating phase. This allowed researchers to register domains the infested host would contact.
The C&C server distributed three modules, which comprise Torpig. These inject these DLLs into the file manager, Internet Explorer, Firefox, and other popular utilities, allowing it to inspect all data handled by these programs. Every twenty minutes, Torpig uploads new data to the command server. In reply to this, the C&C server can either respond with ‘ok’ or a configuration file used for configuration and parameters to perform phishing attacks. These attacks can gain data that would not otherwise be possible by passive monitoring. When the user goes to a site in the configuration file, they will instead be redirected to a site given by an injection server.
Taking over the botnet was fairly simple; domains were registered for a three-week period. Logs were collected from all network data, until a new torpig binary that changed the domain generation algorithm was installed through Mebroot. 70GB of data were collected during the 10-day period that the Torpig botnet was under control.
All bots communicate with the Torpig command server through HTTP Post requests. This requests contains all the collected dat, as well as information about the bot. There are 8 different types of data that Torpig sends out: Mailbox account, email, form data, HTTP account, FTP account, POP account, and Windows passwords.
Attempting to analyze the size of the botnet is somewhat difficult. It can’t be done by merely checking how many IPs connect to the C&C server vecause of NAT and DHCP. However, Torpig contains information for hardware configurations and a mostly-unique ID for each bot. This led to an estimated 182,914 bots in the Torpig botnet. Further analysis was done to find the number of security researchers and search engine bots to get a more accurate number. Security researchers could be found by checking the default hardware configurations of VMWare and other virtualization tools. This gave a final estimate of 182,800 bots. In contrast, the number of IPs connecting to the C&C server was an order of magnitude larger. In the ten days the botnet was taken over, 49,924 new hosts were infected, though there were large spikes on two days.
Torpig is crafted to retrieve information that can easily be monetized. In the ten days, Torpig obtained 8310 accounts at financial institutions. 1660 credit and debit card numbers were also obtained. By pricing these accounts, the estimated value from these ten days is between $83K and $8.3M. In addition to information retrieval, Torpig opens proxies that can be used for spam or other activities, and represents a great deal of bandwidth that can be used in a DOS attack. It logs all other datas, which represents a huge breach of privacy and can be used to look at all chat, email, and other messages sent.
Analysis of the passwords retrieved showed that most were not very high strength, and roughly 28% of users reuse their passwords. This is evidence that the reason these botnets so large is a cultural problem, of people not understanding the consequences of irresponsible computer use.