W32.HLLW.Backzat.G

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Discovered: January 21, 2003
Updated: February 13, 2007 11:56:17 AM
Type: Worm
Systems Affected: Windows


W32.HLLW.Backzat.G is a mass-mailing worm that uses Microsoft Outlook to send itself to all the contacts in the Microsoft Outlook Address Book. It also attempts to spread itself through the Grokster, eDonkey2000, BearShare, Morpheus, and KaZaA file-sharing networks. This worm may distribute itself across the mapped drives and through AIM95, mIRC, and ICQ.

W32.HLLW.Backzat.G deletes the security software from your computer.

The email it sends has the following characteristics:

Subject:  Fw: Hello there.
Message:  Hey, I just recieved a screen saver in the mail and it is really cute. Take a loot.
Attachment: CuteKirby.Scr

This threat is written in the Microsoft C++ programming language and is compressed with UPX.

Antivirus Protection Dates

  • Initial Rapid Release version January 22, 2003
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version January 22, 2003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date January 22, 2003

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

Writeup By: Yana Liu

Discovered: January 21, 2003
Updated: February 13, 2007 11:56:17 AM
Type: Worm
Systems Affected: Windows


When W32.HLLW.Backzat.G runs, it does the following:

  1. Displays this fake message:


  2. Copies itself as:
    • C:\%System%\CuteKirby.Scr
    • C:\%System%\TaskSystemDll.Exe

      NOTES: %System% is a variable. The worm locates the Windows system folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/ME), C:\Windows\System32 (Windows XP), or C:\Winnt\System32 (Windows 2000/NT).

  3. Copies itself as Kirbster.exe to all the drives from D to Z.
  4. Adds the value:

    WinSysStartUpWKbLw C:\%System%\TaskSystemDll.Exe

    to the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

    so that the worm runs when you start Windows.
  5. Creates C:\%Windir%\Kirbybmp.bmp, which is not a malicious bitmap file. It is 1,782 bytes in length.

    NOTE: %Windir% is a variable. The worm locates the Windows installation folder and copies itself to that location. By default, this is C:\Windows or C:\Winnt.
  6. Modifies the value of Wallpaper to:

    Wallpaper C:\%windir%\Kirbybmp.bmp

    in the registry key:

    HKEY_CURRENT_USER\Control Panel\Desktop
  7. Adds the value:

    SCRNSAVE.EXE C:\%system%\CuteKirby.Scr

    in the registry key:

    HKEY_CURRENT_USER\Control Panel\Desktop
  8. Creates C:\%Windir%\KirbyWins.mp3, which is not a malicious Winamp media file. It is 66,003 bytes in length. Then, the worm opens this mp3 file.
  9. Locates the KaZaA transfer folder by retrieving the value from the registry key:

    HKEY_CURRENT_USER\Software\Kazaa\Transfer\DlDir0

    If the KaZaA transfer folder exists, the worm copies itself as:
      • C:\Program Files\Grokster\My Grokster\AFI - 6 to 8.Mp3.Exe
      • C:\Program Files\EDonkey2000\Incoming\Feeder - Under The Weather.Mp3.Exe
      • C:\Program Files\BearShare\Shared\Therion - Nifelheim.Mp3.Exe
      • C:\Program Files\Morpheus\My Shared Folder\PennyWise - Land Of The Free.Mp3.Exe
      • C:\Program Files\ICQ\Shared Files\WinIso - Iso Ripper.Exe
      • C:\My Downloads\ePs2e - PS2 Emulator.Exe
      • <The KaZaA transfer folder>\Rage Against The Machine - Sleep Now In This Fire.Mp3.Exe

        NOTE: The Grokster, eDonkey2000, BearShare, KaZaA, Morpheus, or ICQ software must be installed on the computer for the worm to spread in those networks.

  10. Locates the mIRC folder by retrieving the value from the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Uninstall\mIrc
  11. If mIRC is installed, the worm creates the file Script.ini in the mIRC folder, which the worm uses to send copies of itself to other mIRC users.
  12. Copies itself as C:\Program Files\AIM95\CutiePinkKirby.Scr and enables the AIM95 users to share this file.
  13. Attempts to overwrite all the .exe files with itself. Due to the bugs in the worm code, the worm overwrites only one .exe file in the C:\%Windir% folder each time it runs.
  14. Performs the following, if the system day is Sunday:
    1. Creates the following files:
      • KirbyFlooder.Vbs, which is 88 bytes in length
      • KirbyFlooder.Bat, which is 110 bytes in length
      • C:\Kirbymail.vbs
    2. Uses C:\Kirbymail.vbs to send itself to all the contacts in the Microsoft Outlook Address Book. The email has the following characteristics:

      Subject: Fw: Hello there.
      Message: Hey, I just recieved a screen saver in the mail and it is really cute. Take a loot.
      Attachment: CuteKirby.Scr
    3. Deletes all the files in these folders:
      • C:\PC-Cil~1
      • C:\ToolKit\FindVirus
      • C:\AntiVi~1
      • C:\VS95
      • C:\TBAVW95
      • C:\f-macro
      • C:\eSafen
      • C:\Progra~1\FindVirus
      • C:\Progra~1\FWIN32
      • C:\Progra~1\QuickH~1
      • C:\Progra~1\AntiVi~1
      • C:\Progra~1\Grisoft\AVG6
      • C:\Progra~1\AvPersonal
      • C:\Progra~1\Trojan~1
      • C:\Progra~1\Kasper~1
      • C:\Progra~1\TinyPe~1
      • C:\Progra~1\ZoneLa~1\ZoneAlarm
      • C:\Progra~1\Comman~1\F-PROT95
      • C:\Progra~1\TrendM~1\Pc-cil~1
      • C:\Progra~1\PandaS~1\PandaA~1
      • C:\Progra~1\eSafe\Protect
      • C:\Progra~1\McAfee\McAfee FireWall
      • C:\Progra~1\McAfee\VirusScan
      • C:\Progra~1\Common~1\Symant~1\Script~1
      • C:\Progra~1\Common~1\Symant~1
      • C:\Progra~1\Symantec
      • C:\Progra~1\Norton~2
      • C:\Progra~1\Norton~1
    4. Overwrites all the .doc and .txt files with the text "L0NEw0lf was here..." in the following folders:
      • C:
      • C:\%Windir%
      • C:\%Windir%\System
      • C:\%Windir%\System32


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: Yana Liu

Discovered: January 21, 2003
Updated: February 13, 2007 11:56:17 AM
Type: Worm
Systems Affected: Windows


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

NOTE: If the worm has run and succeeded to delete your Symantec antivirus product, re-install it before you can scan for and delete the
worm. In this situation, first follow the instructions in the "Reversing the changes made to the registry" section, restart the computer, and then re-install your antivirus product.

  1. Update the virus definitions.
  2. Run a full system scan and delete all the files detected as W32.HLLW.Backzat.G. Restore any required files, which the worm overwrote, from a clean backup. Manually delete the files:
    • C:\%windir%\Kirbybmp.bmp.
    • C:\%windir%\KirbyWins.mp3
  3. Reverse the changes made 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. 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.HLLW.Backzat.G, write down the file names, and then click Delete.
  4. Using Windows Explorer, locate and delete the files:
    • C:\%windir%\Kirbybmp.bmp.
    • C:\%windir%\KirbyWins.mp3

3. Reversing the changes made to the registry

CAUTION : Symantec 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 registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

    In the right pane, delete this value:

    WinSysStartUpWKbLw C:\%system%\TaskSystemDll.Exe
  4. Navigate to the registry key:

    HKEY_CURRENT_USER\Control Panel\Desktop

    In the right pane, delete this value:

    SCRNSAVE.EXE C:\%system%\CuteKirby.Scr

    Next, double-click wallpaper

    and delete the text:

    C:\%windir%\Kirbybmp.bmp

    from the Value Data box.
  5. Click Registry, and then click Exit.


Writeup By: Yana Liu