This week, the DOJ and FBI seized five servers that controlled Coreflood-infected computers, the DOJ said in a press release. The agencies also seized 29 domain names used by the Coreflood botnet to communicate with the servers.

In addition, the U.S. Attorney's Office for the District of Connecticut filed a civil complaint Monday against 13 unnamed defendants, alleging that the defendants engaged in wire fraud, bank fraud and illegal interception of electronic communications. The DOJ also obtained search warrants for computer servers across the country, it said.

"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," Shawn Henry, executive assistant director of the FBI's Criminal, Cyber, Response and Services Branch, said in a statement. "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."

Coreflood records computer keystrokes and other private communications, the DOJ said. Coreflood steals user names, 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 case described in court documents, criminals used Coreflood to take over an online banking session and cause the transfer of funds to a foreign account.