A related civil complaint, filed by the government on Monday against 13 "John Doe" defendants, alleged that they have engaged in "wire fraud, bank fraud, and unauthorized interception of electronic communications" by using the botnet, which installed key-logging software to steal people's personal financial information. Criminals used the information to remove money from people's bank accounts via wire transfers.
Authorities said that, as of February 2010, about 2.3 million PCs were infected with Coreflood, and 80% of them were located in the United States. According to court documents, known victims of the botnet have included a Tennessee defense contractor who lost $242,000, a North Carolina investment company that lost $151,000, and a Michigan real estate company that lost $116,000.
Thanks to the temporary restraining order, authorities can swap out the servers powering Coreflood for their own, replacing them with substitute C&C servers run by the government. The court has issued a permanent injunction against the defendants running Coreflood on any computer, and authorizes authorities to install replacement C&C servers wherever they find more Coreflood servers, at least on U.S. soil.
"The seizure of the Coreflood servers and Internet domain names is expected to prevent criminals from using Coreflood or computers infected by Coreflood," said David B. Fein, U.S. attorney for the District of Connecticut, in a statement.
Computers infected by Coreflood regularly attempt to phone home to the C&C server. When they do so, the government's substitute C&C servers will return a command to disable the malware. At the same time, authorities will alert the user's Internet service provider that the PC is infected by Coreflood, and ask the service provider to contact the user and recommend that they install antivirus software to eliminate the infection.
Authorities said that anyone will be able to "opt out" of the temporary restraining order, "if for some reason they want to keep Coreflood running on their computers." They also promised that "at no time will law enforcement authorities access any information that may be stored on an infected computer."
Authorities recently worked with Microsoft to take down the Rustock botnet, backed by a court order that enabled them to physically remove C&C servers from hosting premises. But adding substitute C&C servers is a new tactic. According to a statement from Shawn Henry, executive assistant director of the FBI's criminal, cyber, response, and services branch, "these actions to mitigate the threat posed by the Coreflood botnet are the first of their kind in the United States and reflect our commitment to being creative and proactive in making the Internet more secure."
Similar coordinated-takedown tactics have already been used abroad--to good effect--most notably in the Dutch takedown of the Bredolab botnet. Costin Raiu, director of the global research and analysis team at Kaspersky Lab, speaking at a press event in early 2011, said that the Dutch approach was a model for correctly busting a botnet. In particular, the Dutch authorities monitored Bredolab for a long period of time, then launched a coordinated takedown, first arresting the alleged botnet mastermind, then waiting to see who else took over running the botnet.
"The right way here is to go after not just the botnet, but to arrest the herder--the botnet master--so the Dutch found out who was behind the botnet," said Raiu. Next, they contacted both Romanian and Armenian police, because the suspect had dual nationality. Finally, they waited. When the bot-herder made plans to fly to Armenia, Dutch police requested that they detain him when he landed. Then they waited again, to see if anyone else assumed control of Bredolab.
With Coreflood, it's not clear if U.S. authorities have identified actual suspects--per the 13 "John Doe" defendants--or if they're working with more basic information, such as the IP addresses of computers located abroad. The Department of Justice couldn't be reached for immediate comment.