A malware infection which drew headlines January has returned and is using new techniques to infect and spread amongst users.
Known as Sefnit, the botnet infection was spotted in September of 2013 and triggered alarms earlier this year when researchers warned that millions of systems were likely infected with the malware. Associated with click fraud and bitcoin mining activities, Sefnit was noted for its use of the Tor anonymising network as a means of avoiding detection.
Microsoft researcher Jeff McDonald wrote at the time that the malware was using Tor to hide its command and control servers, directing traffic through the online network before connecting the infected machines with their control servers.
Now, according to researchers with Facebook, the Sefnit infection is back, albeit without the use of a Tor client. Security experts working with the social network spotted the infection spreading in the wild.
This time, say the researchers, the Sefnit malware is operating without the use of Tor, instead establishing direct connections via a secure Plink connection with one or more command and control servers. The malware, which initially tries to hide itself as a Windows Theme system file, operates as a pair of executables.
In a detailed roundup of the infection, the researchers are hoping to provide administrators and security teams with details which can help detect the the new code,which they say appears to have been developed in late March. The researchers listed thirty domains which have already been associated with the malware infections.
Once installed, the malware uses its control servers to receive orders or, download additional payloads.
Such a resurgence of a popular malware samples has been seen before. Often successful infections are repackaged and modified by their original authors or adopted by other cybercriminal groups for new attacks.
Popular kits such as the ZeuS malware have menaced users in for years while constantly changing or receiving tweaks to add new capabilities or avoid detection from antimalware tools and law enforcement groups. ®