The Department of Justice and FBI today announced the filing of a civil complaint, the execution of criminal seizure warrants, and the issuance of a temporary restraining order against a huge international “botnet.”

The botnet is a network of hundreds of thousands of computers infected with a malicious software program known as Coreflood, which installs itself by exploiting a vulnerability in computers running Windows operating systems.

Coreflood allows infected computers to be controlled remotely for the purpose of stealing private personal and financial information from unsuspecting computer users, including users on corporate computer networks, and using that information to steal funds.

The U.S. Attorney's Office for the District of Connecticut filed a civil complaint against 13 "John Doe" defendants, alleging that the defendants engaged in wire fraud, bank fraud, and illegal interception of electronic communications. In addition, search warrants were obtained for computer servers throughout the country, and a seizure warrant was obtained in U.S. District Court for the District of Connecticut for 29 domain names.

Finally, the government obtained a temporary restraining order (TRO), authorizing the government to respond to signals sent from infected computers in the United States in order to stop the Coreflood software from running, thereby preventing further harm to hundreds of thousands of unsuspecting users of infected computers in the United States.

"The seizure of the Coreflood servers and Internet domain names is expected to prevent criminals from using Coreflood or computers infected by Coreflood for their nefarious purposes," said U.S. Attorney David B. Fein for the District of Connecticut. "I want to commend our industry partners for their collaboration with law enforcement to achieve this great result."

"Botnets and the cyber criminals who deploy them jeopardize the economic security of the United States and the dependability of the nation's information infrastructure," said 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."

Particularly harmful

According to court filings, Coreflood is a particularly harmful type of malicious software that records keystrokes and private communications on a computer. Once a computer is infected with Coreflood, it can be controlled remotely from another computer, known as a command and control (C & C) server.

A computer infected by Coreflood and subject to remote control is referred to as a "bot," short for "robot." According to information contained in court filings, the group of all computers infected with Coreflood is known as the Coreflood botnet, which is believed to have been operating for nearly a decade and to have infected more than two million computers worldwide.

Coreflood steals usernames, passwords, and other private personal and financial information allegedly used by the defendants for a variety of criminal purposes, including stealing funds from the compromised accounts. In one example described in court filings, through the illegal monitoring of Internet communications between the user and the user's bank, Coreflood was used to take over an online banking session and caused the fraudulent transfer of funds to a foreign account.

In the enforcement actions announced today, five C & C servers that remotely controlled hundreds of thousands of infected computers were seized, as were 29 domain names used by the Coreflood botnet to communicate with the C & C servers.

As authorized by the TRO, the government replaced the illegal C & C servers with substitute servers to prevent Coreflood from causing further injury to the owners and users of infected computers and other third parties.

While this enforcement action completely disabled the existing Coreflood botnet by seizing control from the criminals who ran it, this does not mean that Coreflood malware or similar forms of malware have been removed from the Internet entirely. Nor does it mean that criminals will not attempt to build another botnet using a different version of the Coreflood malware or other malware. The best defense against such malware, and botnets in general, is for users to ensure their computers are protected by regularly-updated anti-virus security software.

Computer users should ensure they are using security software on their computers and that users regularly update their security and routinely scan their computers for viruses.