The developer behind the Ramnit botnet—a program focused on banking fraud as well as stealing cookies and credentials from its victims—has stripped out the program's infection capabilities and is now focusing on better avoiding anti-malware defenses and improving its botnet management capabilities, Microsoft stated in a March 14 blog post.
Since 2010, the author of Ramnit has frequently updated the program, converting it from a file-infecting virus to a complete banking Trojan capable of clearing out a victim's account. The tactic has helped the botnet go from an outdated threat to a prolific attacker.
"One of the main reasons Ramnit has been successful is its ability to continually update and add new functions to itself," Jimmy Kuo, principal program manager, Microsoft Malware Protection Center, said in an email interview. "This continuous updating has helped it to avoid detection from anti-malware products."
Some botnets see explosive growth, infecting millions of computers, such as ZeroAccess, which has infected more than 2 million computers. Others—such as the 200 botnets used to eavesdrop on governments and corporations—limit themselves to a few thousand systems and succeed in remaining under security firms' collective radar.
Most active botnets evolve over time, and the developer behind Ramnit frequently updates the botnet to stay ahead of defenders.
The individual or group behind Ramnit has focused on steadily improving the program and making the malware harder to detect and remove. In the latest version, for example, Ramnit uses an extremely comprehensive blacklist of filenames used by antivirus vendors to block the execution of security software. The malware also uses encryption to prevent modules from being detected before they are unpacked by the software. Finally, Ramnit has modules that help the developers' troubleshoot problems by sending back error reports.
"It looks like the troubleshooting module has become a common feature in recently developed botnets," Microsoft stated in the blog post. "The malware authors are analyzing the error reports and making the botnet component more stable."
First detected in 2010, Ramnit evolved in August 2011 from being a rather-outdated virus—spreading from computer to computer by infecting files—to stealing financial and Facebook credentials. Many features appear to have been copied from the Zeus banking Trojan, such as the ability to sniff network connections and inject code into the Web sites displayed on a victim's computer.
By the end of 2011, Ramnit had infected approximately 800,000 systems, according to security-intelligence firm Seculert. Microsoft had added the program to its malware removal tool that year, but by 2012, the number of infections grew by about a quarter, Microsoft said, suggesting it has reached 1 million systems.
The developers of Ramnit have focused on standard man-in-the-browser and Web-injection techniques, where an infected machine will modify a financial institution's pages that are displayed in victims' browsers, to enable the criminals to steal users' log-on information and then money from victim's account. The techniques cannot be detected by the bank, unless the institution is looking closely for anomalous transactions.