W32.HLLW.Nettrash

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Discovered: January 12, 2004
Updated: February 13, 2007 12:51:15 PM
Also Known As: Backdoor.NetTrash, Backdoor/NetTrash.10.a [Kasper
Type: Trojan Horse, Worm
Systems Affected: Windows


W32.HLLW.Nettrash allows unauthorized access to your computer. This Trojan horse also has components to spread using peer-to-peer file sharing, Microsoft Outlook, and IRC.

Note: Virus definitions dated January 13, 2004 will detect this as Backdoor.NetTrash.

Antivirus Protection Dates

  • Initial Rapid Release version January 13, 2004
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version January 13, 2004
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date January 14, 2004

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

Writeup By: Maryl Magee

Discovered: January 12, 2004
Updated: February 13, 2007 12:51:15 PM
Also Known As: Backdoor.NetTrash, Backdoor/NetTrash.10.a [Kasper
Type: Trojan Horse, Worm
Systems Affected: Windows


W32.HLLW.Nettrash is written in Visual Basic. It allows unauthorized access and control of a compromised computer. It allows the attacker to specify how much RAM to allocate.

By default, the Trojan uses TCP ports 23005 and 23006, but this is configurable.

Some of the functions available to the attacker are:

  • Moving and changing the mouse appearance and functionality
  • Key logging
  • Gathering system information
  • Changing keyboard layout and functions
  • Disabling the keyboard
  • Hiding and showing the taskbar
  • Hiding and showing the desktop
  • Hiding and showing the Start button
  • Hiding and showing the system tray and clock
  • Changing screen settings
  • File and directory functions (delete, write, modify)
  • Uploading and downloading files
  • Locking system
  • Opening and closing the CD door
  • Beeping
  • Printing files
  • Allocating the amount of RAM (can cause system crash)
  • Disconnecting Internet connection(s)
  • Restarting or shutting down the computer

    In addition, this threat contains the functionality to spread using peer-to-peer file sharing, IRC, and Microsoft Outlook.

    When W32.HLLW.Nettrash runs, it performs the following actions:
    1. Copies itself to C:\Windows, both as the original file name and a hidden, read-only file named Login.scr. The path to the C:\Windows folder is hard-coded and does not depend on system variables.

    2. Registers itself to run as a process named "User32."

    3. Adds the values:

      "User32" = <path to original filename>

      <original file name> = <path to original filename>

      (For example, "NetTrash" = "C:\mydir\nettrash.exe")

      to the registry key:

      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run

      so that the Trojan runs when you start Windows.

    4. Copies itself to C:\Windows\Start menu\Programs\startup. This path is hard-coded and does not depend on system variables.

    5. Adds the line:

      run=<original file name of Trojan>

      to the [windows] section of the C:\Windows\Win.ini file.

      If the Windows installation folder is not C:\Windows, the existing Win.ini file is not modified.

    6. Prepends the original file name to the default key of the registry value:

      HKEY_CLASSES_ROOT\exefile\shell\open\command

      so that any time you run a file that has an .exe extension, the Trojan is executed first.

      For example, "Default"="NetTrash.exe "%1" %* "


      Note: The Trojan only modifies this value if it was able to copy itself to the C:\Windows folder. If C:\Windows does not exist on your system, this value is not modified.

    7. Copies itself to C:\Program Files\KaZaA\My Shared Folder (if the folder exists) as:
      • Bin Laden funny flash.exe
      • Black Jack.exe
      • counter strike keygen.exe
      • Dcom microsoft patch.exe
      • full casino games.exe
      • half life keygen.exe
      • hl + cs key generator.exe
      • Madona sex game.exe
      • Msblast Fix.exe
      • Msblast Remover.exe
      • msn bomber.exe
      • pockemon sex.exe

    8. Searches for C:\mIRC or C:\mIRC32 and adds a hidden Script.ini, which attempts to exploit random users on the mIRC server, befown.dynu.com, by sending them the Trojan file.

    9. Attempts to create email messages as follows:

      Subject: One of the following:
      angry at me??
      We need to talk...!
      What's the problem?
      How are you??
      You need help?
      What's happening???
      RE: Why you not replying??
      Need help!
      Check this out!
      Why are you so
      Funny for you...

      Message: One of the following:

      I tried to reach you at MSN Messenger but you weren't online! I got something important to tell you!

      You said you needed help huh? Well attached file (You'll find what I wanted to tell you there!) Ok. Reply as soon as possible!
      Bye!

      Where have you been all the time??? I tried to call you but you weren't home! Anyway, see the attached file! It's important! I got the solution for your problem! Just open the attached file and see what's in it ;)

      I need your help! I'm in a very difficault position right now. I can't decide how good the file is from rate 0 To 5! I need your opinion on it, so check it out (It's attached to this message!) and tell me what you think from rate 0 To 5!

      Why are you so angry at me? What have I done to you?? I only want you to check this file out; It describes my opinion about you. Please check it, you won 't be dissapointed ;) Hope to hear from you soon :)

      Attachment: One of the following:
      Funny
      Nice_pic
      arabic sex
      Nice Song
      Interesting
      ReadMe
      Information

      The attached file will have the extension of .com, .jpg, .mpg, .txt, .doc, .mp3, .asp, .htm, or .php.

    10. After creating the mail message, the worm component attempts to mail itself to everyone in the Microsoft Outlook address book.


  • 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: Maryl Magee

    Discovered: January 12, 2004
    Updated: February 13, 2007 12:51:15 PM
    Also Known As: Backdoor.NetTrash, Backdoor/NetTrash.10.a [Kasper
    Type: Trojan Horse, Worm
    Systems Affected: Windows


    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.HLLW.Nettrash.
    4. Delete the values that were added to the registry.
    5. Edit the Win.ini file (Windows 95/98/Me).
    For specific details on each of these steps, read the following instructions.


    Notes:
    • If the Trojan has not yet run—that is, the Trojan's file was copied to your computer but has not run—you should be able to follow the instructions in sections 1 through 3, which discuss detecting and removing this file.
    • If the Trojan has run, in some cases you will not be able to follow these instructions, as the modifications that the Trojan made will prevent you from doing so. In this situation, first follow the instructions in section 4 to edit the registry. After you complete those instructions, follow the steps in sections 1 through 3..



    WARNING: If you are running Windows 95/98/Me, do not restart your computer until you have removed the Trojan.


    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:
    Note: When you are completely finished with the removal procedure and are satisfied that the threat has been removed, re-enable 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. 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.HLLW.Nettrash, click Delete.

    4. Deleting the value from the registry

    Copying Regedit.exe to Regedit.com and editing the registry
    Because the Trojan modified the registry so that the Trojan runs when you run the .exe files, first make a copy of the Registry Editor as a file with the .com extension, and then run the file.
    1. Do one of the following, depending on the version of Windows you are running:
      • Windows 95/98 users:
        1. Click Start.
        2. Point to Programs.
        3. Click the MS-DOS Prompt. (A DOS window opens at the C:\Windows prompt.) Proceed to step B of this section.

      • Windows Me users:
        1. Click Start.
        2. Point to Programs.
        3. Point to Accessories.
        4. Click the MS-DOS Prompt. (A DOS window opens at the C:\Windows prompt.) Proceed to step B of this section.

      • Windows NT/2000 users:
        1. Click Start, and then click Run.
        2. Type command, and then press Enter. (A DOS window opens.)
        3. Type cd \winnt, and then press Enter.
        4. Go to step B of this section.

      • Windows XP users:
        1. Click Start, and then click Run.
        2. Type command, and then press Enter. (A DOS window opens.)
        3. Type the following:

          cd\
          cd \windows

          Press Enter after typing each one.
        4. Proceed to step B of this section.

    2. Type copy regedit.exe regedit.com

      and then press Enter.

    3. Type start regedit.com

      and then press Enter. (The Registry Editor opens in front of the DOS window.)

      After you finish editing the registry, exit the Registry Editor, and then exit the DOS window as well.

    4. Before continuing, 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 keys only. For instructions, read the document, "How to make a backup of the Windows registry."

    5. Navigate to and select the key:

      HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command

      NOTE: The HKEY_LOCAL_MACHINE\Software\Classes key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with a .exe extension from running. Make sure that you completely browse through this path until you reach the \command subkey.

      Modify the HKEY_LOCAL_MACHINE\Software\Classes\exefile\shell\open\command subkey, shown in the following figure:

      <<=== NOTE: Modify this key.

    6. In the right pane, double-click the (Default) value.
    7. Delete the current value data, and then type:

      "%1" %*

      That is, type the characters: quote-percent-one-quote-space-percent-asterisk.

      NOTES
      • Under Windows 95/98/Me/NT, the Registry Editor automatically encloses the value within quotation marks. When you click OK, the (Default) value should look exactly like this:

        ""%1" %*"  
      • Under Windows 2000/XP, the additional quotation marks will not appear. When you click OK, the (Default) value should look exactly like this:

        "%1" %*
      • Make sure that you completely delete all the value data in the command key before typing the correct data. If you leave a space at the beginning of the entry, any attempt to run the program files will result in the error message, "Windows cannot find .exe." If this occurs, restart the entire process from the beginning of this document and make sure that you completely remove the current value data.

    8. Navigate to the key:

      HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

    9. In the right pane, delete the value:

      "User32"="<path to original file name>"

    10. In the right pane, delete the value:

      "<original app name>" = "<path to original file name>"

    11. Exit the Registry Editor.

    5. Editing the Win.ini file
    If you are running Windows 95/98/Me, follow these steps:
    1. The function you perform depends on your operating system:
      • Windows 95/98: Go to step B.
      • Windows Me: If you are running Windows Me, the Windows Me file-protection process may have made a backup copy of the Win.ini file that you need to edit. If this backup copy exists, it will be in the C:\Windows\Recent folder. Symantec recommends that you delete this file before continuing with the steps in this section. To do this:
        1. Start Windows Explorer.
        2. Browse to and select the C:\Windows\Recent folder.
        3. In the right pane, select the Win.ini file and delete it. The Win.ini file will be regenerated when you save your changes to it in step F.

    2. Click Start, and then click Run.
    3. Type the following, and then click OK.

      edit c:\windows\win.ini

      (The MS-DOS Editor opens.)

    4. In the [windows] section of the file, look for a line similar to:

      run=<original file name of Trojan>

    5. If this line exists, delete everything to the right of run=.

    6. Click File, and then click Save.
    7. Click File, and then click Exit.



    Writeup By: Maryl Magee