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TROJ_VILSEL.ACE

October 09, 2012
 Analysis by: MarfelTi
 Modified by: Cris Nowell Pantanilla
 ALIASES:

VirTool:WinNT/Emold.gen!A (Microsoft); Trojan.Win32.Vilsel.vdy (Kaspersky); Generic.dx!oxh (McAfee)

 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

This Trojan deletes the a certain registry key to disable restarting in safe mode.

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:

34,820 bytes

File Type:

EXE

Memory Resident:

No

Initial Samples Received Date:

28 Jun 2011

Payload:

Deletes a registry key

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 copies of itself into the affected system:

  • %System%\logon.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.)

Autostart Technique

This Trojan 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 logon.exe"

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

NOTES:
It deletes the following registry keys to disable restarting in safe mode:

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\
SafeBoot

  SOLUTION

Minimum Scan Engine:

8.900

FIRST VSAPI PATTERN FILE:

8.254.03

FIRST VSAPI PATTERN DATE:

28 Jun 2011

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 delete files detected as TROJ_VILSEL.ACE using either the Startup Disk or Recovery Console

[ Learn More ]

Step 3

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 logon.exe"
      To: Shell = "Explorer.exe"

Step 4

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

NOTES:

To Restore Safe Boot Registry Settings:

  1. Open Notepad. To do this, click Start>Run, type Notepad in the text box provided, then press Enter.
  2. Copy and paste the following script:

    For Windows 2000:


    For Windows XP:


    For Windows 2003:
  3. Save this file as C:\RESTORE.REG..
  4. Click Start>Run again, type C:\RESTORE.REG in the text box provided, then press Enter.
  5. Click Yes at the prompt of the message box to execute the .REG file.


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