Select local site

| Japanese | Simplified Chinese | Traditional Chinese (Hong Kong) | Traditional Chinese (Taiwan)

F-Secure Malware Information Pages: Backdoor:W32/PcClient.YW
[Summary] | [Disinfection] | [Detailed Description] | [Detection]

Name : Backdoor:W32/PcClient.YW
Alias:DR/PcClient.Gen, Trojan.Dropper.CI
Size:varies
Type:Backdoor
Category:Malware
Platform:W32
Date of Discovery:March 08, 2007
Radar

Summary
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.
Back to the Top

Disinfection

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.
Back to the Top

Detailed Description
Once the Backdoor:W32/PcClient.YW had been  executed, it will drop its components in the following path and filename:
  • %programfiles%\internet explorer\connection wizard\zhyrikwo.dll - backdoor
  • %programfiles%\internet explorer\connection wizard\zhyrikwo.drv - keylogger

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:
  • %programfiles%\internet explorer\connection wizard\zhyrikwo.sys - rootkit
It modifies the following known registry entry as its autostart technique:

Data before:
  • [HKLM\SYSTEM\CurrentControlSet\Services\sens\Parameters]
ServiceDll = %sysdir%\sens.dll

Data after:
  • [HKLM\SYSTEM\CurrentControlSet\Services\sens\Parameters]
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:
  • [HKLM\System\ControlSet001\Services\zhyrikwo]
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:

  • updating itself
  • remote execution

This malware connects to the following site:

http://dynsev5299.2mydns.com/i[BLOCKED]x.asp
Back to the Top

Detection

F-Secure Anti-Virus detects this malware with the following updates:

[FSAV_Database_Version]

Version = 2007-03-07_10.
Back to the Top



F-Secure Corporation

Last Modified: March 09, 2007