Analysis by: Jennifer Gumban
ALIASES:

TrojanDownloader:Win32/Stegvob.D (Microsoft), Trojan-Downloader.Win32.Agent.xhdy (Kaspersky), Downloader-FFF (McAfee)

 PLATFORM:

Windows 2000, Windows Server 2003, Windows XP (32-bit, 64-bit), Windows Vista (32-bit, 64-bit), Windows 7 (32-bit, 64-bit)

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

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted: No

  • In the wild: Yes

  OVERVIEW

Infection Channel: Downloaded from the Internet, Dropped by other malware, , Propagates via removable drives

This worm arrives by connecting affected removable drives to a system. It arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

As of this writing, the said sites are inaccessible.

It requires its main component to successfully perform its intended routine.

  TECHNICAL DETAILS

File Size: 1,039,369 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 08 Apr 2013
Payload: Downloads files

Arrival Details

This worm arrives by connecting affected removable drives to a system.

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

Autostart Technique

This worm enables its automatic execution at every system startup by dropping the following copies of itself into the Windows Common Startup folder:

  • %User Startup%\search.cmd

(Note: %User Startup% is the current user's Startup folder, which is usually C:\Windows\Profiles\{user name}\Start Menu\Programs\Startup on Windows 98 and ME, C:\WINNT\Profiles\{user name}\Start Menu\Programs\Startup on Windows NT, and C:\Documents and Settings\{User name}\Start Menu\Programs\Startup.)

Propagation

This worm drops the following copies of itself in all physical and removable drives:

  • {drive letter}:\Photo.scr

Download Routine

This worm connects to the following URL(s) to download its component file(s):

  • http://www.{BLOCKED}est.ru/load.php
  • http://www.{BLOCKED}est.ru/get.php

It saves the files it downloads using the following names:

  • %Application Data%\temp.cmd

(Note: %Application Data% is the current user's Application Data folder, which is usually C:\Documents and Settings\{user name}\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Roaming on Windows Vista and 7.)

As of this writing, the said sites are inaccessible.

Other Details

This worm requires its main component to successfully perform its intended routine.

NOTES:

This worm has a folder icon and opens the following folders to trick users that it is a legitimate folder:

  • %User Profile%\Pictures (Windows Vista and higher versions)
  • %User Profile%\My Documents\My Pictures (Versions lower than Windows Vista)

  SOLUTION

Minimum Scan Engine: 9.300
FIRST VSAPI PATTERN FILE: 9.872.06
FIRST VSAPI PATTERN DATE: 22 Apr 2013
VSAPI OPR PATTERN File: 9.873.00
VSAPI OPR PATTERN Date: 23 Apr 2013

Step 1

Before doing any scans, Windows XP, Windows Vista, and Windows 7 users must disable System Restore to allow full scanning of their computers.

Step 2

Restart in Safe Mode

[ Learn More ]

Step 3

Search and delete this file

[ Learn More ]
There may be some 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 Startup%\search.cmd
  • {drive letter}:\Photo.scr
  • %Application Data%\temp.cmd

Step 4

Restart in normal mode and scan your computer with your Trend Micro product for files detected as WORM_TOPHOS.SM. 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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