Analysis by: kathleenno
ALIASES:

Trojan:Win32/Opachki.F (Microsoft); Backdoor.Win32.IRCNite.cbb (Kaspersky)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 54,784 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 29 Mar 2011
Payload: Drops files, Downloads files

Installation

This Trojan drops the following files:

  • %User Profile%\pizda_ntload.dll - detected as TROJ_DROPPER.PXH

(Note: %User Profile% is the current user's profile folder, which is usually C:\Windows\Profiles\{user name} on Windows 98 and ME, C:\WINNT\Profiles\{user name} on Windows NT, and C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003.)

It drops the following copies of itself into the affected system:

  • %System%\userinit.exe
  • %System%\dllcache\userinit.exe

(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.)

It drops the following non-malicious file:

  • %User Temp%\nxfsss.bak

(Note: %User Temp% is the current user's Temp folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Temp on Windows 2000, XP, and Server 2003.)

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
rundll32 = "%User Profile%\userinit.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
rundll32 = "%System%\ntdevice.exe"

It modifies the following registry entries to ensure it automatic execution at every system startup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "explorer.exe %System%\ntdevice.exe"

(Note: The default value data of the said registry entry is Explorer.exe .)

Other System Modifications

This Trojan deletes the following files:

  • %System%\userinit.exe
  • %System%\dllcache\userinit.exe

(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.)

It adds the following registry entries:

HKEY_CURRENT_USER\Software\Microsoft
adver_id = "0"

Download Routine

As of this writing, the said sites are inaccessible.

Other Details

This Trojan attempts to access the following websites to download files, which are possibly malicious:

  • {BLOCKED}er1.co.cc

  SOLUTION

Minimum Scan Engine: 8.900

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

Remove malware files dropped/downloaded by TROJ_OPACHKI.W

    • TROJ_DROPPER.PXH

Step 3

Identify and delete files detected as TROJ_OPACHKI.W using either the Startup Disk or Recovery Console

[ Learn More ]

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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • rundll32 = %User Profile%\userinit.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • rundll32 = %System%\ntdevice.exe
  • In HKEY_CURRENT_USER\Software\Microsoft
    • adver_id = 0

Step 5

Restore this modified 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\Winlogon
    • From: Shell = explorer.exe %System%\ntdevice.exe
      To: Explorer.exe

Step 6

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.
  • %User Temp%\nxfsss.bak

Step 7

Scan your computer with your Trend Micro product to delete files detected as TROJ_OPACHKI.W. 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.

Step 8

Restore this file from backup only Microsoft-related files will be restored. If this malware/grayware also deleted files related to programs that are not from Microsoft, please reinstall those programs on you computer again.

  • %System%\userinit.exe
  • %System%\dllcache\userinit.exe


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