Analysis by: Maydalene Edsel Salvador
ALIASES:

Generic PWS.y!1td (NAI), Trojan horse PSW.OnlineGames4.UJC.dropper (AVG), Trojan-Dropper.Win32.Dapato (Ikarus), Win32/Briba.AB (NOD32)

 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: Backdoor

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

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

It deletes itself after execution.

  TECHNICAL DETAILS

File Size: 47,616 bytes
File Type: EXE
Memory Resident: Yes
Initial Samples Received Date: 30 Aug 2012

Arrival Details

This backdoor 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 backdoor drops the following files:

  • %Application Data%\wmdmps.dll

(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.)

Autostart Technique

This backdoor adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
rundll32.exe = "rundll32.exe "%Application Data%\wmdmps.dll",ReportErro"

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://download.{BLOCKED}k.com/download.php?dw
  • http://download.{BLOCKED}k.com/version.php

It deletes itself after execution.

  SOLUTION

Minimum Scan Engine: 9.300
VSAPI OPR PATTERN File: 9.361.01
VSAPI OPR PATTERN Date: 30 Aug 2012

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.  
  • %Application Data%\wmdmps.dll

Step 4

Delete this 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_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
    • rundll32.exe = "rundll32.exe "%Application Data%\wmdmps.dll",ReportErro"

Step 5

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