Analysis by: Christopher Daniel So
ALIASES:

TrojanDownloader:Win32/Small.gen!AO (Microsoft), Trojan.Gen (Symantec), Generic.dx!thd (McAfee), Trojan.Win32.Buzus.ezmn (Kaspersky), Trojan.Win32.Generic!BT (Sunbelt), Trj/Buzus.AH (Panda), TR/Dropper.Gen (AntiVir), Trojan horse Generic18.ARGJ (AVG), Trojan.Win32.Buzus (Ikarus), Trojan W32/Suspicious_Gen2.BURTB (Norman), Trojan.Buzus.ezmn (Quickheal), Trojan.Win32.Buzus.eogm (VBA32)

 PLATFORM:

Windows 2000, Windows XP, Windows Server 2003

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

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted: Yes

  • In the wild: Yes

  OVERVIEW

It opens the non-malicious URL http://www.irs.gov/pub/irs-pdf/f941.pdf to hide its malicious routines from the user.

It registers the downloaded .DLL file as a Browser Helper Object (BHO) by executing a specific command-line.

It starts the service Application Layer Gateway Service2.

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.

It executes downloaded files whose malicious routines are exhibited by the affected system. As of this writing, the said sites are inaccessible.

  TECHNICAL DETAILS

File Size: 112,640 bytes
File Type: PE
Memory Resident: No
Initial Samples Received Date: 30 Jul 2010
Payload: Downloads files

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 adds the following mutexes to ensure that only one of its copies runs at any one time:

  • MSO7ACD026FA3844258AE657C3AB37E675Dago

Download Routine

This Trojan accesses the following websites to download files:

  • http://{BLOCKED}.{BLOCKED}.240.87/1.jpg
  • http://{BLOCKED}.{BLOCKED}.240.87/2.jpg

It saves the files it downloads using the following names:

  • %Windows%\inf\alg.exe
  • %Windows%\inf\AcroIEHelper.dll

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

It executes downloaded files :

  • %Windows%\inf\alg.exe

(Note: %Windows% is the Windows folder, which is usually C:\Windows or C:\WINNT.)

whose malicious routines are exhibited by the affected system.

As of this writing, the said sites are inaccessible.

Other Details

This Trojan does the following:

  • It opens the non-malicious URL http://www.irs.gov/pub/irs-pdf/f941.pdf to hide its malicious routines from the user.
  • It registers the downloaded file %Windows%\inf\AcroIEHelper.dll as a Browser Helper Object (BHO) by executing the following command-line:
    • regsvr32 /i /s %Windows%\inf\AcroIEHelper.dll
  • It starts the service Application Layer Gateway Service2.

  SOLUTION

Minimum Scan Engine: 8.900
VSAPI PATTERN File: 7.366.11
VSAPI PATTERN Date: 07 Aug 2010
VSAPI PATTERN Date: 8/7/2010 12:00:00 AM

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

Delete these Browser Helper Object (BHO) registry keys

[ Learn More ]
%Windows%\inf\AcroIEHelper.dll

Step 3

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

Step 4

Search and delete these files

[ Learn More ]
There may be some component 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.
  • %Windows%\inf\alg.exe
  • %Windows%\inf\AcroIEHelper.dll


Did this description help? Tell us how we did.