After a single attempt to resurrect the ZeroAccess botnet, the criminal group controlling the network of approximately 1.3 million compromised PCs has signaled to defenders its intention to move on.
This week, Microsoft, which continues to monitor the ZeroAccess botnet, detected a new message to the remaining computers' infected ZeroAccess malware. Unlike a previous attempt to update the botnet with new orders, the message did not try to re-target infected computers, but contained the message, "WHITE FLAG," according to Microsoft.
The message likely means that the criminals behind the botnet have decided to give up on resurrecting the botnet and will likely try to move on to other activities, Richard Boscovich, assistant general counsel for Microsoft's Digital Crimes Unit, told eWEEK. The message initially confused the analyst monitoring the ZeroAccess botnet, he said.
"One of the guys on our team was looking at it; he just thought it was gibberish, but then said, that's odd, all the fraud has stopped," Boscovich said. "What probably happened—and this is a bit speculative on my part, but jives with what we are seeing—the speed by which we were able to coordinate with international law enforcement, and how quickly the Europeans moved, basically convinced the ZeroAccess group that it is just too hot to continue."
ZeroAccess is the eighth botnet that Microsoft has acted to shut down under its Microsoft Active Response for Security (MARS) project, which has used a combination of legal and technical tactics to identify the critical parts of the botnets' infrastructure and obtain court orders to seize or disrupt those components.
On Dec. 5, Microsoft, its industry partners, and U.S. and European law-enforcement agencies seized 18 computers used by the ZeroAccess botnet, also known as Sirefef. Unlike previous takedowns, the servers seized by law-enforcement agents were not command-and-control servers but fraud-control servers, which provide infected systems with instructions on how to redirect users' ad clicks to ZeroAccess-friendly advertising networks. Microsoft had already filed a civil lawsuit against the controller of ZeroAccess and won a court order allowing it to seize the servers.
"Because of the sophistication of the threat, Microsoft and its partners do not expect to fully eliminate the ZeroAccess botnet," Microsoft stated on its blog about the initial takedown. "However, we do expect this legal and technical action will significantly disrupt the botnet’s operation by disrupting the cyber-criminals’ business model and forcing them to rebuild their criminal infrastructure, as well as preventing victims’ computers from committing the fraudulent schemes."
Within 24 hours of the takedown, the ZeroAccess group attempted to update infected computers on the peer-to-peer network with the addresses of a second set of fraud-control servers. Microsoft and U.S. and European law-enforcement agencies have monitored communications on the peer-to-peer botnet, detected the update and immediately shut down the new IP addresses, Boscovich said. Initial estimates put the size of the ZeroAccess botnet around 2 million computers, but it has since shrunk to 1.3 million.
Following the "white flag" message, Microsoft shut down its civil lawsuit against the cyber-crime group, which made millions of dollars in a click-fraud scheme fueled by the more than a million compromised PCs. Criminal investigations against the group will continue.
The ZeroAccess takedown followed Microsoft's November announcement of its Cybercrime Center, a group that brings together the people and technology to fight the criminal use of computer technology.