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W32.Imaut.BH

Discovered: November 09, 2007
Updated: November 09, 2007 12:04:44 PM
Type: Worm
Infection Length: 1,396,988 bytes
Systems Affected: Windows


Summary

W32.Imaut.BH is a worm that spreads through Yahoo! Instant Messenger and removable drives. It may also spread through network shares protected by weak passwords.

Antivirus Protection Dates
  • Initial Rapid Release version November 09, 2007 revision 004
  • Latest Rapid Release version May 10, 2012 revision 007
  • Initial Daily Certified version November 09, 2007 revision 002
  • Latest Daily Certified version May 10, 2012 revision 019
  • Initial Weekly Certified release date November 14, 2007

Writeup By: Hiroshi Shinotsuka


Technical Description

When the worm executes, it creates the following files:

  • %System%\SVICHOOST.exe
  • %Windir%\SVICHOOST.exe


Next, the worm creates the following registry entries so that it executes whenever Windows starts:
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\"Shell" = "Explorer.exe SVICHOOST.exe"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\"Yahoo Messengger" = "%System%\SVICHOOST.exe"


The worm modifies the following registry entries to disable the registry editor and Windows Task Manager:
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System\"DisableTaskMgr" = "1"
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System\"DisableRegistryTools" = "1"


It also modifies the following registry entries:
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\"NofolderOptions" = "1"
  • HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Schedule\"AtTaskMaxHours" = "0"


The worm then deletes the following registry subkeys:
  • HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BkavFw
  • HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\IEProtection


Next, the worm contacts the following site to download a configuration file:
[http://]gaig0isaigon.t35.com

It saves the above file to the following location:
%System%\setting.ini

The worm searches for an open Yahoo! Instant Messenger window and sends the following messages chosen at random:
  • E may, vao day coi co con nho nay ngon lam
  • Vao day nghe bai nay di ban
  • Vao day nghe bai nay di ban
  • Biet tin gi chua, vao day coi di
  • Trang Web nay coi cung hay, vao coi thu di
  • Toi di lang thang lan trong bong toi buot gia, ve dau khi da mat em roi? Ve dau khi bao nhieu mo mong gio da vo tan... Ve dau toi biet di ve dau?
  • Khoc cho nho thuong voi trong long, khoc cho noi sau nhe nhu khong. Bao nhieu yeu thuong nhung ngay qua da tan theo khoi may bay that xa...
  • Tha nguoi dung noi se yeu minh toi mai thoi thi gio day toi se vui hon. Gio nguoi lac loi buoc chan ve noi xa xoi, cay dang chi rieng minh toi...
  • Loi em noi cho tinh chung ta, nhu doan cuoi trong cuon phim buon. Nguoi da den nhu la giac mo roi ra di cho anh bat ngo...
  • Tra lai em niem vui khi duoc gan ben em, tra lai em loi yeu thuong em dem, tra lai em niem tin thang nam qua ta dap xay. Gio day chi la nhung ky niem buon...


The above messages also contain the following link:
[http://]nhatquanglan1.0catch.com

Next, the worm attempts to close any windows containing the following strings, if they exist:
  • Bkav2006
  • System Configuration
  • Registry
  • Windows Task


It then attempts to end the following processes:
  • cmd.exe
  • game_y.exe


The worm attempts to shut down the computer if the following window exists:
FireLion

The worm then searchs for removable drives attached to the computer and attempts to copy itself as the following file:
%DriveLetter%\New Folder.exe

Next, the worm searches for the following registry subkey for shares to copy itself to:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\WorkgroupCrawler\Shares

If a share is found it copies itself to the following location:
%CurrentFolder%\New Folder.exe

It also copies itself as the following file:
%CurrentFolder%.exe

For example, if the folder %CurrentFolder%\Exa\mple exists, the worm creates the following file:
%CurrentFolder%\Exa\mple\mple.exe

The worm sets a command to execute the following file every day at 9:00 AM:
%System%\SVICHOOST.exe

Recommendations

Writeup By: Hiroshi Shinotsuka


Removal

The following instructions pertain to all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

  1. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Run a full system scan.
  4. Delete any values added to the registry.

For specific details on each of these steps, read the following instructions.

1. To disable System Restore (Windows Me/XP)
If you are running Windows Me or Windows XP, we recommend that you temporarily turn off System Restore. Windows Me/XP uses this feature, which is enabled by default, to restore the files on your computer in case they become damaged. If a virus, worm, or Trojan infects a computer, System Restore may back up the virus, worm, or Trojan on the computer.

Windows prevents outside programs, including antivirus programs, from modifying System Restore. Therefore, antivirus programs or tools cannot remove threats in the System Restore folder. As a result, System Restore has the potential of restoring an infected file on your computer, even after you have cleaned the infected files from all the other locations.

Also, a virus scan may detect a threat in the System Restore folder even though you have removed the threat.

For instructions on how to turn off System Restore, read your Windows documentation, or one of the following articles:
  • How to disable or enable Windows Me System Restore
  • How to turn off or turn on Windows XP System Restore

Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable System Restore by following the instructions in the aforementioned documents.

For additional information, and an alternative to disabling Windows Me System Restore, see the Microsoft Knowledge Base article: Antivirus Tools Cannot Clean Infected Files in the _Restore Folder (Article ID: Q263455).

2. To update the virus definitions
Symantec Security Response fully tests all the virus definitions for quality assurance before they are posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Running LiveUpdate, which is the easiest way to obtain virus definitions.

    If you use Norton AntiVirus 2006, Symantec AntiVirus Corporate Edition 10.0, or newer products, LiveUpdate definitions are updated daily. These products include newer technology.

    If you use Norton AntiVirus 2005, Symantec AntiVirus Corporate Edition 9.0, or earlier products, LiveUpdate definitions are updated weekly. The exception is major outbreaks, when definitions are updated more often.


  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. You should download the definitions from the Symantec Security Response Web site and manually install them.

The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions . For detailed instructions read the document: How to update virus definition files using the Intelligent Updater .

3. To run a full system scan
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.

    For Norton AntiVirus consumer products: Read the document: How to configure Norton AntiVirus to scan all files.

    For Symantec AntiVirus Enterprise products: Read the document: How to verify that a Symantec Corporate antivirus product is set to scan all files.


  2. Run a full system scan.
  3. If any files are detected, follow the instructions displayed by your antivirus program.
Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode . Once you have restarted in Safe mode, run the scan again.
After the files are deleted, restart the computer in Normal mode and proceed with the next section.

Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

Title: [FILE PATH]
Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

4. To delete the value from the registry
Important: Symantec strongly recommends that you back up the registry before making any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify the specified subkeys only. For instructions refer to the document: How to make a backup of the Windows registry .
  1. Click Start > Run.
  2. Type regedit
  3. Click OK.

    Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.

  4. Navigate to and delete the following registry entries:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\"Shell" = "Explorer.exe SVICHOOST.exe"
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\"Yahoo Messengger" = "%System%\SVICHOOST.exe"

  5. Restore the following registry entries to their previous values, if required:

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System\"DisableTaskMgr" = "1"
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System\"DisableRegistryTools" = "1"
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\"NofolderOptions" = "1"
    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Schedule\"AtTaskMaxHours" = "0"

  6. Restore the following registry subkeys from a clean backup, if required:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BkavFw
    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run\IEProtection

  7. Exit the Registry Editor.

    Note: If the risk creates or modifies registry subkeys or entries under HKEY_CURRENT_USER, it is possible that it created them for every user on the compromised computer. To ensure that all registry subkeys or entries are removed or restored, log on using each user account and check for any HKEY_CURRENT_USER items listed above.

Writeup By: Hiroshi Shinotsuka

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