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Category: Malware

Type: Backdoor

Aliases: Backdoor.Pcclient, Backdoor.Win32.PcClient, Backdoor:Win32/PcClient (Microsoft) , BKDR_PCCLIENT.VK (Trend Micro), Backdoor.Formador (Symantec)


A remote administration utility which bypasses normal security mechanisms to secretly control a program, computer or network.


Automatic action

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Technical Details

Backdoor:W32/PcClient.VK is seen in the wild as the payload file installed on a host machine by a specially crafted Microsoft PowerPoint file that contains exploit code.

When run, PcClient.VK attempts to hide processes, files, registry data and network connections, allows the attacker to perform arbitrary actions on machine, and steals sensitive information from an infected computer.


Once execution of PcClient.VK been initiated, its executable component will drop the following hard-coded files in the Windows System directory:

  • Ybrcuugm.d1l - Backdoor
  • Ybrcuugm.dll - Keylogger

Note: the file size of Ybrcuugm.d1l 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's processes, registry entries and files:

  • %sysdir%\drivers\Ybrcuugm.sys

Moreover it also hides some network traffic that the PcClient.VK uses.


Part of the malware's payload is that is logs all the keystrokes made by the user and saves it to the following file:

  • %sysdir%\log.txt

It then sends this file to a remote hacker.


The malware's backdoor routine is injected into svchost.exe, which is capable doing the following:

  • updating itself
  • remote execution

This malware connects to the following site:

  • http://baas.8866.org/[BLOCKED]ex.asp

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

Data before:

  • [HKLM\SYSTEM\CurrentControlSet\Services\dmserver\Parameters] ServiceDll = %sysdir%\dmserver.dll

Data after:

  • [HKLM\SYSTEM\CurrentControlSet\Services\dmserver\Parameters] ServiceDll = %sysdir%\Ybrcuugm.d1l

In order for the system to work normally, Ybrcuugm.dll will execute its malicious routine and then pass the correct parameter to the original dmserver.dll.

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

  • [HKLM\System\ControlSet001\Services\Ybrcuugm] ImagePath= C:\WINDOWS\system32\drivers\Ybrcuugm.sys