"In February 2011, we successfully collaborated with CDMON, a registrar, to gain control of a Zeus botnet C&C server, thereby rendering it ineffective," said Trend Micro security researchers David Sancho and Rainer Link in a blog post.
According to a report (pdf) released by Trend Micro that detailed the takedown in greater detail, this particular Zeus botnet targeted customers of 15 banks in the United States, South America, and Europe, as well as multiple online payment providers, including eBay and PayPal.
"The lack of coherence regarding the targeted banks and the locations of the infected computers suggests that the botmaster just left a default configuration while spreading the Trojan around his own geographical area," according to the report. "This was a sign that he was still an amateur."
Zeus is a crimeware toolkit that's used to build botnets and steal sensitive financial information from people's PCs. There are multiple "Zeus botnets" in the wild, each of which reports back to the botmaster that created it.
Indeed, according to the Zeus Tracker, which is monitoring more than 500 Zeus C&C servers, there are at least 44 Zeus C&C servers running in Russia, 35 in the United States, 29 in Romania, and 28 in the Ukraine. As that suggests, even though Zeus also appears to have merged with SpyEye, a former competitor, people are still using the standalone Zeus malware toolkit.
The botnet sinkholed by Trend Micro appeared to have originated in the Americas. "We found that over 95% of the inbound requests to the C&C server came from South America, particularly from Mexico," said the Trend Micro researchers. "This indicates that the bot may have originated from Latin America or was created using the Spanish language. Its creator may have decided to target banks in Mexico and Chile as well, as these often still used single-factor authentication to secure their customers' accounts."
For the takedown, domain registrar CDMON -- through which the botmaster had registered the sites for his Zeus-driven attacks -- helped Trend Micro impersonate the real C&C server. "CDMON was kind enough to replace the server's original address with that of our own machine," according to the Trend Micro report. "This was enough to tell the bot clients that they should communicate with us instead of the cybercriminal." The security company said it collected three weeks' worth of data for analysis before deactivating the botnet.