BKDR_THOPER.AO

February 01, 2013
 Analysis by: Jaime Benigno Reyes
 ALIASES:

Backdoor:Win32/Thoper.E (Microsoft), Trojan.Win32.Tvt.hb (Kaspersky)

 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 requires its main component to successfully perform its intended routine.

  TECHNICAL DETAILS

File Size:

242,176 bytes

File Type:

DLL

Memory Resident:

Yes

Initial Samples Received Date:

29 Jan 2013

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:

  • %ProgramData%\Microsoft\PDA\SS.LOG (Windows Vista and 7 only)
  • %System Root%\Users\All Users\Microsoft\PDA\SS.LOG (Windows Vista and 7 only)
  • %AppDataLocal%\VirtualStore\ProgramData\Microsoft\PDA\SS.LOG (Windows Vista and 7 only)
  • %System Root%\Documents and Settings\All Users\Microsoft\PDA\SS.LOG (versions other than Windows Vista and 7)

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This is usually C:\ProgramData in Windows Vista and 7, or C:\Program Files on Windows 2000, XP (32-bit), and Server 2003, or C:\Program Files (x86) on Windows XP (64-bit).. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista and 7.)

It creates the following folders:

  • %ProgramData%\Microsoft\PDA (Windows Vista and 7 only)
  • %System Root%\Users\All Users\Microsoft\PDA (Windows Vista and 7 only)
  • %AppDataLocal%\VirtualStore\ProgramData (Windows Vista and 7 only)
  • %AppDataLocal%\VirtualStore\ProgramData\Microsoft (Windows Vista and 7 only)
  • %AppDataLocal%\VirtualStore\ProgramData\Microsoft\PDA (Windows Vista and 7 only)
  • %System Root%\Documents and Settings\All Users\Microsoft (versions other than Windows Vista and 7)
  • %System Root%\Documents and Settings\All Users\Microsoft\PDA (versions other than Windows Vista and 7)

(Note: %ProgramData% is a version of the Program Files folder where any user on a multi-user computer can make changes to programs. This is usually C:\ProgramData in Windows Vista and 7, or C:\Program Files on Windows 2000, XP (32-bit), and Server 2003, or C:\Program Files (x86) on Windows XP (64-bit).. %System Root% is the root folder, which is usually C:\. It is also where the operating system is located.. %AppDataLocal% is the Local Application Data folder, which is usually C:\Documents and Settings\{user name}\Local Settings\Application Data on Windows 2000, XP, and Server 2003, or C:\Users\{user name}\AppData\Local on Windows Vista and 7.)

Other System Modifications

This backdoor adds the following registry keys as part of its installation routine:

HKEY_CLASSES_ROOT\SS

HKEY_CLASSES_ROOT\SS\PROXY

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
SS

HKEY_LOCAL_MACHINE\SOFTWARE\Classes\
SS\PROXY

Other Details

This backdoor connects to the following possibly malicious URL:

  • http://{BLOCKED}76.{BLOCKED}.net

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

  SOLUTION

Minimum Scan Engine:

9.300

FIRST VSAPI PATTERN FILE:

9.688.04

FIRST VSAPI PATTERN DATE:

29 Jan 2013

VSAPI OPR PATTERN File:

9.689.00

VSAPI OPR PATTERN Date:

30 Jan 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

Scan your computer with your Trend Micro product and note files detected as BKDR_THOPER.AO

Step 3

Restart in Safe Mode

[ Learn More ]

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. Before you could do this, you must restart in Safe Mode. For instructions on how to do this, you may refer to this page If the preceding step requires you to restart in safe mode, you may proceed to edit the system registry.

 
  • HKEY_CLASSES_ROOT\SS
  • HKEY_LOCAL_MACHINE\SOFTWARE\Classes\SS

Step 5

Search and delete the files detected as BKDR_THOPER.AO

*Note: Some component files may be 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.

To stop the malware/grayware from running when certain files are opened:

For Windows 2000, Windows XP, and Windows Server 2003:

  1. Right-click Start then click Search....
  2. In the Named input box, type the name of the file that was detected earlier.
  3. In the Look In drop-down list, select My Computer then press Enter.
  4. Once located, select the file then press SHIFT+DELETE to delete it.

For Windows Vista and Windows 7:

  1. Click Start>Computer.
  2. In the Search Computer input box, type the name of the file detected earlier, and press Enter.
  3. Once located, select the file then press SHIFT+DELETE to delete it.
    *Note: Read the following Microsoft page if these steps do not work on Windows 7.

Step 6

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.
  • %ProgramData%\Microsoft\PDA\SS.LOG (Windows Vista and 7 only)
  • %System Root%\Users\All Users\Microsoft\PDA\SS.LOG (Windows Vista and 7 only)
  • %AppDataLocal%\VirtualStore\ProgramData\Microsoft\PDA\SS.LOG (Windows Vista and 7 only)
  • %System Root%\Documents and Settings\All Users\Microsoft\PDA\SS.LOG (versions other than Windows Vista and 7)

Step 7

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