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Discovered: February 02, 2003
Updated: February 13, 2007 11:42:46 AM
Also Known As: W32/Gemel.worm [McAfee]
Type: Worm
Systems Affected: Windows

W32.HLLW.Gemel is a worm that attempts to spread through the Grokster, Morpheus, and KaZaA file-sharing networks. This worm also spreads through ICQ and floppy disks.

This threat has several versions, and all the versions are written in the Microsoft Visual Basic programming language. It may be compressed with UPX or tElock.

Antivirus Protection Dates

  • Initial Rapid Release version February 03, 2003
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version February 03, 2003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date February 05, 2003

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

Technical Description

When W32.HLLW.Gemel runs, it does the following:

  1. Deletes the following system files:
    • C:\Windows\Regedit.exe
    • C:\Windows\System\Msconfig.exe
    • C:\Command.com

  2. Creates a 652 byte text file and opens the text file with Notepad. The file name is one of the following:
    • C:\Windows\Torres_Gemelas.txt
    • C:\Windows\World_Trade_Center.txt

      NOTE: This text file is not viral itself, and as such, Symantec antivirus products do not detect it. Manually delete it if found.

  3. Creates the C:\Windows\Guindows folder and copies itself to this folder as one of the following:
    • Gedzac.exe
    • Zacker.exe

  4. Adds one of the following values:

    GEDZAC C:\Windows\Guindows\GEDZAC.exe
    Zacker C:\Windows\Guindows\Zacker.exe

    to the registry key:


    so that the worm runs each time you start Windows.
  5. Modifies the Value Data of two values, as shown here:

    RegisteredOwner Kuasanagui


    RegisteredOrganization GEDZAC


    RegisteredOrganization Zacker

    in the following registry keys:

  6. Adds one of the following values:


    to the registry key:

  7. Copies itself to the following folders using many different names carried by the worm:
    • C:\Program Files\Grokster\My Grokster
    • C:\Program Files\Morpheus\My Shared Folder
    • C:\Program Files\ICQ\shared files
    • C:\Program Files\KaZaA\My Shared Folder
    • C:\Archiv~1\Grokster\My Grokster
    • C:\Archiv~1\Morpheus\My Shared Folder
    • C:\Archiv~1\ICQ\shared files
    • C:\Archiv~1\KaZaA\My Shared Folder

      Some examples of these file names are:
      • WinZip
      • Norton Antivirus 2002 Crack
      • Microsoft Windows XP Crack
      • ICQ & MSN Hack-Tool
      • Worm Generator
      • Hentai XXX ScreenSaver
      • Osama Movie
      • Star Wars Episodio II
      • Britney_XXX_Pasion_Ana

        The copies of the worm may have one of the following extensions:
        • .exe
        • .scr
        • .bat
        • .pif
        • .com

  8. Periodically attempts to copy itself as A:\Atentados Terrorista.

NOTE: The worm can spread only when Grokster, Morpheus, KaZaA, or ICQ have been installed in the system.


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.


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

  1. Update the virus definitions.
  2. Restart the computer in Safe mode.
  3. Run a full system scan and delete all the files detected as W32.HLLW.Gemel. Delete the text file that was created by the worm.
  4. Restore the following files from known, clean backup copies, if the worm deleted them.
    • C:\Windows\Regedit.exe
    • C:\Windows\System\Msconfig.exe
    • C:\Command.com
  5. Remove the values that the worm added to the registry.
For specific details on each of these procedures, read the following instructions.

1. 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 the 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), in the "Protection" section, at the top of this writeup.
  • 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), in the "Protection" section, at the top of this writeup.

    The Intelligent Updater virus definitions are available here. For detailed instructions on how to download and install the Intelligent Updater virus definitions from the Symantec Security Response Web site, click here.

2. Restarting the computer in Safe mode
All the Windows 32-bit operating systems, except Windows NT, can be restarted in Safe mode. For instructions on how to do this, read the document, "How to start the computer in Safe mode ."

3. Scanning for and deleting the infected files
  1. Start your Symantec antivirus program, and make sure that it is configured to scan All Files.
  2. Run a full system scan.
  3. If any files are detected as being infected with W32.HLLW.Gemel, click Delete.
  4. Delete either of these files, if found:
    • C:\Windows\Torres_Gemelas.txt
    • C:\Windows\World_Trade_Center.txt

4. Restoring the deleted files
Restore the following files from known, clean backup copies, if the worm deleted them:
  • C:\Windows\Regedit.exe
  • C:\Windows\System\Msconfig.exe
  • C:\Command.com
5. Removing the values that from the registry

CAUTION : Symantec strongly recommends 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 the specified keys only. Read the document, "How to make a backup of the Windows registry ," for instructions.
  1. Click Start, and then click Run. (The Run dialog box appears.)
  2. Type regedit, and then click OK. (The Registry Editor opens.)
  3. Navigate to the following key:

  4. In the right pane, delete any of these values:

    GEDZAC C:\Windows\Guindows\GEDZAC.exe
    Zacker C:\Windows\Guindows\Zacker.exe
  5. Navigate to each of the following keys:

  6. In the right pane, modify the Value Data of these values to the correct information for your computer:

  7. In the right pane, delete any of these values:

  8. Exit the Registry Editor.

Writeup By: Yana Liu