Analysis by: Christopher Daniel So
ALIASES:

Trojan:Win32/VB.ACS;W32/Refroso.AGEA!tr;W32/VB.CYB

 PLATFORM:

Windows 2000, XP, Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

Infection Channel: Spammed via email

This Trojan arrives as an attachment to email messages spammed by other malware/grayware/spyware or malicious users.

It bears the file icons of certain applications to avoid easy detection and consequent removal. It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 43,008 bytes
File Type: EXE
File Compression: UPX
Memory Resident: No
Initial Samples Received Date: 06 Nov 2010
Payload: Drops files

Arrival Details

This Trojan arrives as an attachment to email messages spammed by other malware/grayware/spyware or malicious users.

Installation

This Trojan bears the file icons of the following applications:

  • Microsoft Word

It deletes itself after execution.

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CLASSES_ROOT\idid

It modifies the following registry key(s)/entry(ies) as part of its installation routine:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows NT\CurrentVersion\Winlogon
Shell = "Explorer.exe rundll32.exe {random file name} {random string}"

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

Dropping Routine

This Trojan drops the following files:

  • %System%\{random file name} - detected as TROJ_DLOADR.SMVE

(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.)

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI PATTERN File: 7.596.10
VSAPI PATTERN Date: 06 Nov 2010
VSAPI PATTERN Date: 11/6/2010 12:00:00 AM

Step 1

For Windows ME and XP 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_REFROSO.GB

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 rundll32.exe {random file name} {random string}
      To: Shell=Explorer.exe

Step 4

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.

  • In HKEY_CLASSES_ROOT
    • idid

Step 5

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