Analysis by: Cris Nowell Pantanilla
 Modified by: Rika Joi Gregorio
 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:

  • Threat Type: Worm

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This worm drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

  TECHNICAL DETAILS

File Size: 167,403 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 01 Oct 2009

Installation

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

  • %system%\drivers\svchost.exe

It drops the following component file(s):

  • %User Temp%\rs.bat

(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, or C:\Users\{user name}\AppData\Local\Temp on Windows Vista and 7.)

Other System Modifications

This worm modifies the following registry entries:

HKLM\SYSTEM\CurrentControlSet\
Services\wuauserv
ImagePath = "%System%\drivers\svchost.exe"

(Note: The default value data of the said registry entry is %System%\svchost.exe -k netsvcs.)

Propagation

This worm drops the following copy(ies) of itself in all removable drives:

  • setup.exe

It drops an AUTORUN.INF file to automatically execute the copies it drops when a user accesses the drives of an affected system.

The said .INF file contains the following strings:

[AutoRun]
open=setup.exe
shellexecute=setup.exe
shell\\Auto\\command=setup.exe

  SOLUTION

Minimum Scan Engine: 9.300

Step 1

Identify and terminate files detected as WORM_DOWNAD.AN

[ Learn More ]
  1. Windows Task Manager may not display all running processes. In this case, please use a third-party process viewer, preferably Process Explorer, to terminate the malware/grayware/spyware file. You may download the said tool here.
  2. 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.
  3. If the detected file is not displayed in either Windows Task Manager or Process Explorer, continue doing the next steps.

Step 2

Restore these modified registry values

[ Learn More ]

Important:Editing the Windows Registry incorrectly can lead to irreversible system malfunction. Please do this only if you know how to or you can seek your system administrator's help. You may also check out this Microsoft article first before modifying your computer's registry.

  • In HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wuauserv
    • From: ImagePath = "%System%\drivers\svchost.exe"
      To: ImagePath = "%System%\svchost.exe -k netsvcs"

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 Temp%\rs.bat

Step 4

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