Analysis by: Sabrina Lei Sioting
ALIASES:

Backdoor:Win32/PcClient.ZL (Microsoft), Backdoor.Trojan (Symantec), Backdoor.Win32.PcClient (Sunbelt), W32/PcClient.AC.gen!Eldorado (Fprot), Trojan.Win32.Genome (Ikarus),

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

  TECHNICAL DETAILS

File Size: 39,424 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 20 Aug 2012

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following component file(s):

  • %System%\Prcmxnq.src

(Note: %System% is the Windows system folder, which is usually C:\Windows\System on Windows 98 and ME, C:\WINNT\System32 on Windows NT and 2000, or C:\Windows\System32 on Windows XP and Server 2003.)

Autostart Technique

This Trojan registers itself as a system service to ensure its automatic execution at every system startup by adding the following registry entries:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_MEDIACENTER\
0000
Service = "MediaCenter"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MediaCenter
ImagePath = "%System%\svchost.exe -k krnlsrvc"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MediaCenter
DisplayName = "MS Media Control Center"

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MediaCenter\Parameters
ServiceDll = "%System%\Prcmxnq.src"

It registers as a system service to ensure its automatic execution at every system startup by adding the following registry keys:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Enum\Root\LEGACY_MEDIACENTER

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\
Services\MediaCenter

Other System Modifications

This Trojan adds the following registry entries as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\SvcHost
krnlsrvc = "MediaCenter"

Other Details

This Trojan connects to the following possibly malicious URL:

  • http://www.{BLOCKED}.com/ip2008.txt

  SOLUTION

Minimum Scan Engine: 9.200

Step 1

For Windows XP and Windows Server 2003 users, before doing any scans, please make sure you disable System Restore to allow full scanning of your computer.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Delete this registry key

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Enum\Root
    • LEGACY_MEDIACENTER
  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
    • MediaCenter

Step 4

Delete this registry value

[ Learn More ]

Important: Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this step only if you know how or you can ask assistance from your system administrator. Else, check this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SvcHost
    • krnlsrvc = "MediaCenter"

Step 5

Search and delete this file

[ Learn More ]
There may be some component files that are hidden. Please make sure you check the Search Hidden Files and Folders checkbox in the More advanced options option to include all hidden files and folders in the search result. %System%\Prcmxnq.src

Step 6

Restart in normal mode and scan your computer with your Trend Micro product for files detected as TROJ_NETBOT.L. If the detected files have already been cleaned, deleted, or quarantined by your Trend Micro product, no further step is required. You may opt to simply delete the quarantined files. Please check this Knowledge Base page for more information.


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