TROJ_DLDR.ACE

 Analysis by: Sabrina Lei Sioting

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  TECHNICAL DETAILS

File Size:

42,496 bytes

File Type:

EXE

Memory Resident:

Yes

Initial Samples Received Date:

05 Apr 2011

Installation

This Trojan drops the following copies of itself into the affected system:

  • %system root%\userini.exe

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\Policies\
Explorer\Run
userini = %WINDOWS%\explorer.exe:userini.exe

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
userini = %WINDOWS%\explorer.exe:userini.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
Explorer\Run
userini = %WINDOWS%\explorer.exe:userini.exe

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
userini = %WINDOWS%\explorer.exe:userini.exe

Other System Modifications

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

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer
id = {hexadecimal}

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Explorer
remove = %current folder%\{malware name}.exe

  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

Identify and terminate files detected as TROJ_DLDR.ACE

[ Learn More ]
  1. If the detected file is displayed in either Windows Task Manager or Process Explorer but you cannot delete it, restart your computer in safe mode. To do this, refer to this link for the complete steps.
  2. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 3

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\Policies\Explorer\Run
    • userini = %WINDOWS%\explorer.exe:userini.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • userini = %WINDOWS%\explorer.exe:userini.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\policies\Explorer\Run
    • userini =%WINDOWS%\explorer.exe:userini.exe
  • In HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    • userini = %WINDOWS%\explorer.exe:userini.exe
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
    • id = {hexadecimal}
  • In HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
    • remove = %currentfolder%\{malwarename}.exe

Step 4

Scan your computer with your Trend Micro product to delete files detected as TROJ_DLDR.ACE. 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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