Miscreants have created a strain of malware capable of removing rootkits from compromised PCs, only to install almost undetectable backdoor code of its own.
The Pandex Trojan stops previously installed rootkits from working by removing their hooks into system calls. Pandex then installs its own rootkit component, detected by Trend Micro as Pushu-AC.
Rootkits are a type of malware that hide their presence on infected PCs, making them more dangerous than typical viruses. By operating below the level of traditional malware scanning tools, rootkits are able to carry out covert functions, for example keystroke-logging, without detection.
Virus writers have competed for control of vulnerable PCs several times in the past. For example, in 2005 separate groups of hackers released a barrage of worms in a battle to seize control of Windows PCs vulnerable to the then infamous Windows Plug-and-Play (PnP) vulnerability.
The Bozori worm was programmed to remove infections by earlier versions of the Zotob worm and other malware, so it could take control of a compromised computer for itself. A family of IRC bots that exploit the same Microsoft Plug and Play vulnerability likewise tried to remove competing PnP bots.
In early 2004, variants of the Netsky worm designed to remove Bagle and MyDoom infections from compromised PCs were released into the wild amid an ongoing war of words between rival VXers.
More recently, a turf war erupted between the creators of the Storm worm and rival gangs.
The Pandex Trojan updates this dishonourable tradition with code that replaces stealthier malware infections.
More background on the latest twist in the ongoing "virus writers at war" series can be found in an analysis by Trend Micro here. ®