Europol, in collaboration with Dutch authorities, the U.S. FBI and private security companies, have seized the domain names used to control a botnet called Beebone.
The police action Wednesday included a so-called botnet sinkholing operation that involved redirecting domains used by the botnet's command-and-control servers to a server controlled by security companies.
Such an action prevents attackers from controlling the botnet and also gives authorities a chance to identify victims whose computers are now connecting to the sinkhole server.
Information about the botnet will be distributed to ISPs and CERTs [computer emergency response teams] from around the world so they can notify victims and help them clean their systems, Europol said Thursday in a press release.
Compared to some other botnets, Beebone was not large. Initial figures suggest that it's made up of about 12,000 computers, but the final count may be higher.
Since the beginning of the year, Symantec has detected about 30,000 attempted infections by Beebone a month. The U.S., South Africa, Brazil, Mexico and India have the most infected computers.
The Beebone malware, also known as Changeup, is a polymorphic worm that has been around since 2009. It's particularly dangerous because it's used as a malware distribution platform.
Over the years Beebone has been used to distribute more than a dozen computer backdoors, worms, Trojans and other malicious programs, according to an entry in Microsoft's malware database.
Beebone gets installed on systems through drive-by downloads -- Web-based attacks that exploit vulnerabilities in browsers -- but it's also distributed by the Vobfus worm. Beebone itself also installs Vobfus, creating a malware infection loop.
"We will continue our efforts to take down botnets and disrupt the core infrastructures used by cybercriminals to carry out a variety of crimes," said Europol's deputy director of operations, Wil van Gemert. "Together with the EU member states and partners around the globe, our aim is to protect people worldwide against these criminal activities."
Symantec offers a free tool that can detect and clean Beebone/Changeup infections.