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Discovered: July 13, 2003
Updated: February 13, 2007 12:03:46 PM
Also Known As: W32/Gruel-A [Sophos], W32/Fakerr@MM [McAfee], Win32.Gruel [CA]
Type: Worm
Systems Affected: Windows

W32.Gruel@mm is a worm that spreads by email and file-sharing networks. Its payload includes changing user passwords, hiding drive C, and making numerous changes to the system registry.

The email has the following characteristics:
Subject: Microsoft Windows Critical Update.
Attachment: Windows Critical Update 088562.exe
Subject: Symantec: New serious virus found
Attachment: Symantec_Norton_Tool.exe
Subject: Microsoft Windows Critical Update
Attachment: AntiVirus_Patch.exe

Symantec Security Response has received reports that email messages, which falsely claim to have been sent by Symantec, have been sent to numerous email addresses.

These messages may contain an attached file that the message claims is a removal tool for W32.Gruel@mm. There is currently no such tool, and the message is not from Symantec. Symantec never sends unsolicited removal tools by email.

If you receive this or a similar message, delete the message without opening the attached file.

The text of the false message is:

From: "Symantec Corporation"<security@symantec.com>
Subject: Symantec: New Serious Virus found.

Norton Security Response, has detected a new virus in the Internet. For this reason we
made this tool attachement, to protect your computer from this serious virus. Due to the number of submissions
received from customers, Symantec Security Response has upgraded this threat to a Category
5 (Maximum ).

Prevention, using the W32.Gruel@mm Tool:
To prevent or remove W32.W32.Gruel@mm , apply this attachment tool as quickly as possible. This is the easiest way to
remove/prevent this threat.

Technical Details:
Also Known As: W32.Gruel@mm , W32.KillerGuate
Type: Virus
Infection Length: 45,195 bytes (zip file), 45,528 bytes (executable) (45KB approx)
Systems Affected: Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Me, Windows 2003
Systems Not Affected: Macintosh, OS/2, UNIX, Linux

Additional information:
Security Response has received many submissions of corrupted W32.W32.Gruel@mm . A specific detection for this type of
infected file has been added as W32.W32.Gruel@mm . This detection is available in virus definitions dated June 12
2003. Be sure to delete the files detected as W32.W32.Gruel@mm .

Note: If you believe your computer may already be infected or just want to protect it agains W32.W32.Gruel@mm , please
download this tool now.

Symantec Corporation.
Last Updated on: July 13, 2003 04:55:35 PM

Antivirus Protection Dates

  • Initial Rapid Release version July 14, 2003
  • Latest Rapid Release version August 05, 2017 revision 019
  • Initial Daily Certified version July 14, 2003
  • Latest Daily Certified version August 06, 2017 revision 001
  • Initial Weekly Certified release date July 16, 2003

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

Writeup By: Maryl Magee

Discovered: July 13, 2003
Updated: February 13, 2007 12:03:46 PM
Also Known As: W32/Gruel-A [Sophos], W32/Fakerr@MM [McAfee], Win32.Gruel [CA]
Type: Worm
Systems Affected: Windows

When W32.Gruel@mm is run, it performs the following actions:

  1. Deletes, or attempts to delete, the following files:
    • C:\Autoexec.bat
    • C:\Config.sys
    • C:\WINNT\System32\*.dll
    • C:\WINNT\System32\Ntoskrnl.exe
    • C:\WINNT\System32\Command.com
    • C:\WINNT\Regedit.exe
    • C:\Windows\System32\Ntoskrnl.exe
    • C:\Windows\System32\Command.com
    • C:\Windows\Regedit.exe
    • C:\WINNT\System32\*.exe
    • C:\WINNT\System32\*.com
    • C:\WINNT\System32\*.ocx
    • C:\Windows\System32\*.dll
    • C:\Windows\System32\*.ocx
    • C:\Windows\System32\*.exe
    • C:\Windows\System32\*.com

  2. Copies itself as the Hidden system file, C:\Rundll32.exe.

  3. Copies itself to C:\windows\Program Files\Kazaa\My Shared Folder\Windows XP KeyGen 2.5.exe.

  4. Changes the Value data of the (Default) value to:

    <filename of worm> %1

    the following registry keys and values:







    As a result of these changes, the worm runs every time one of the aforementioned program types is executed.

  5. Sets the following registry keys and values:



    "DevicePath" ="C:\Proyecto1.exe"



    HKEY_CURRENT_USER\Software\kIlLeRgUaTe 1.03

  6. Displays a false message that Windows has found an error and asks you to submit the error to Microsoft. There are two buttons displayed in this "warning" message, "Send Error" and "Send and Close."
    • If you click "Send Error," a fake error log is displayed.
    • If you try to cancel the message, the message is repeatedly displayed. Clicking "Back" returns you to the original "warning" message.
    • If you click "Send and Close" the following actions occur:
      • Multiple Control Panel windows open.
      • The CD-ROM drive opens
      • A message from the author of this threat is displayed, and this message cannot be moved or closed.
      • The System Tray is disabled.
      • The Task Bar disappears.
      • Drive C is no longer visible and all the icons disappear.
      • Only open windows remain. The message windows, which the worm generates, obscure them.

  7. Attempts to mail itself to all the addresses in the Microsoft Outlook Address book.
    The email is formatted as follows:

    Subject: Microsoft Windows Critical Update.

    Message body:
    Critical Update: The Microsoft Windows updates found on this patch include fixes to following Windows operating systems: Any update that is critical to the operation of your computer is considered a Critical Update, and is automatically selected for installation during the scan for available updates. This patch is provided to help resolve known issues, and to protect your computer from known security vulnerabilities and all kinds of viruses. Whether a patch applies to your operating system, software programs, or hardware, it is listed in the Critical Updates category, like this patch attached. For Support please contact us at support@microsoft.com.

    Attachment: Windows Critical Update 088562.exe
    Attachment: AntiVirus_Patch.exe


    Subject: Symantec: New serious virus found

    Message body:
    Norton Security Response: has detected a new virus in the Internet. For this reason we made this tool attachement, to protect your computer from this serious virus. Due to the number of submissions received from customers, Symantec Security Response has upgraded this threat to a Category 5 (Maximum )

    Attachment: Symantec_Norton_Tool.exe


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: Maryl Magee

Discovered: July 13, 2003
Updated: February 13, 2007 12:03:46 PM
Also Known As: W32/Gruel-A [Sophos], W32/Fakerr@MM [McAfee], Win32.Gruel [CA]
Type: Worm
Systems Affected: Windows

What you need to do depends on whether W32.Gruel@mm has actually executed.

If W32.Gruel@mm has already executed
If W32.Gruel@mm has run, it is possible that you will no longer be able to start Windows. (The damage the worm does will vary with both the operating system and the installation path.) Even if you can start Windows, once W32.Gruel@mm runs, it makes numerous changes to the registry and attempts to delete the system files.

In this situation, you must replace the deleted files and the Windows registry either from a clean backup, or by re-installing the operating system.

Once you have replaced the registry with a clean copy and restored any missing system files, update the virus definitions and run a full system scan as described in the next section.

If W32.Gruel@mm has not yet executed
If your Symantec antivirus product detects W32.Gruel@mm, delete it. If you suspect that the W32.Gruel@mm file exists on your hard drive, but has not yet executed, follow these steps:

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 and delete all the files detected as W32.Gruel@mm.

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

1. Disabling 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:
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. Updating 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: These virus definitions are posted to the LiveUpdate servers once each week (usually on Wednesdays), unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, refer to the Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted on U.S. business days (Monday through Friday). You should download the definitions from the Symantec Security Response Web site and manually install them. To determine whether definitions for this threat are available by the Intelligent Updater, refer to the Virus Definitions (Intelligent Updater).

    The Intelligent Updater virus definitions are available: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected as infected with W32.Gruel@mm, click Delete.

Writeup By: Maryl Magee