Ramnit started out in 2010 as a computer worm capable of infecting EXE, DLL, HTM, and HTML files. However, over time it evolved into an information-stealing Trojan that's distributed in a variety of ways.
Ramnit is capable of hijacking online banking sessions, stealing session cookies which can then be used to access accounts on various sites, copying sensitive files from hard drives, giving attackers remote access to infected computers and more.
Researchers from antivirus vendor Symantec described the malware program as "a fully-featured cybercrime tool" in a blog post Wednesday and said that it infected over 3.2 million computers over its five years of existence.
Symantec, Microsoft and threat intelligence firm AnubisNetworks assisted Europol and law enforcement investigators from Germany, Italy, the Netherlands, and the U.K. in disrupting the cyberinfrastructure that was used to control the Ramnit botnet.
The operation involved the seizure of servers in four countries and the filing of a lawsuit last week in a U.S. federal court by Microsoft and the Financial Services Information Sharing and Analysis Center. Three hundred domain addresses used by the botnet's operators have also been seized.
Law enforcement and the private sector need to work together to protect people online, said David Finn, associate general counsel and executive director of the Microsoft Cybercrime Center, in a blog post. "That's because the complexity of fighting cybercrime is bigger than any one company or organization. It requires a diverse set of skills, including sophisticated computer forensics, big data analysis and legal strategy."
According to Symantec, the Ramnit botnet was still very active and consisted of around 350,000 compromised computers when the takedown operation was launched. The most affected countries are India with 27 percent of the victims, Indonesia with 18 percent and Vietnam with 12 percent. The U.S. is in fifth place, accounting for 6 percent of infected systems.
Symantec released a stand-alone tool that allows users to check their computers for Ramnit infections and clean them.