Name :	Backdoor:W32/PcClient.YW
Size:	varies
Category:	Malware
Type:	Backdoor
Platform:	W32
Date of Discovery:	March 08, 2007

Backdoor:W32/PcClient.YW attempts to hide processes, files, and registry data. It allows the attacker to perform arbitrary actions on the infected machine. Backdoor:W32/PcClient.YW has a rootkit functionality and steals sensitive information from an infected computer.

Detection and Disinfection of Rootkits

If the rootkit is not detected or it is hidden and FSAV cannot detect its file, it is still possible to detect the malicious activity by scanning the system with a generic rootkit scanner, such as F-Secure BlackLight. More information about F-Secure BlackLight Rootkit Elimination Technology can be found here:

http://www.f-secure.com/blacklight/

The BlackLight utility is also able to disinfect computers that are infected by rootkits.

Once the Backdoor:W32/PcClient.YW had been  executed, it will drop its components in the following path and filename:


Note: the file size of zhyrikwo.dll might vary due to garbage code appended at the end of the file.


It will also drop the following driver that will communicate with the .dll files in order to hide the malware processes, registry entries and files:

It modifies the following known registry entry as its autostart technique:

Data before:

ServiceDll = %sysdir%\sens.dll

Data after:

ServiceDll = %programfiles%\internet explorer\connection wizard\zhyrikwo.dll


The file zhyrikwo.dll will intercept any access to the original file, sens.dll. as a stealth mechanism, and after executing its malicious routines, will transfer the correct parameters to sens.dll.


It also adds the following autostart registry entry for the driver:

ImagePath= %programfiles%\internet explorer\connection wizard\zhyrikwo.sys


Note: This rootkit can be detected by F-Secure's BlackLight.


Part of its payload is that it logs all the keystrokes made by the user and sends this file to a remote hacker.

Another part of the payload is that it has a backdoor component. The backdoor routine is injected into svchost.exe, which is capable of doing the following:


This malware connects to the following site:

http://dynsev5299.2mydns.com/i[BLOCKED]x.asp