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Discovered: March 08, 2003
Updated: February 13, 2007 11:43:55 AM
Also Known As: W32/Deloder-A [Sophos], WORM_DELODER.A [Trend], Win32.Deloder Worm [CA], W32/Deloder.worm [McAfee]
Type: Worm
Systems Affected: Windows

While Symantec Security Response is seeing an increase in submissions of W32.HLLW.Deloder, Symantec DeepSight Threat Management System has shown an overall decrease in activity on port 445. Security Response will continue to monitor this threat, and take action as appropriate.

W32.HLLW.Deloder is a network-aware worm that attempts to connect to a target host, using TCP port 445. This worm affects Windows 2000 and Windows XP only.

If the worm makes a successful connection, it copies the file, Inst.exe, to locations that are hard-coded in the worm. Inst.exe is a backdoor Trojan component that is detected as Backdoor.Dvldr . Then, W32.HLLW.Deloder will load from the Startup folder when you start Windows.

W32.HLLW.Deloder attempts to launch several remote services, which:

  • Copies and executes the backdoor Trojan
  • Copies and executes the worm
  • Deletes the default shares
  • Changes the attributes of the worm and backdoor Trojan to Read only

The worm exists as the Dvldr32.exe file and is packed with ASPack.

Antivirus Protection Dates

  • Initial Rapid Release version March 09, 2003
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version March 09, 2003
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date March 09, 2003

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

Technical Description

When W32.HLLW.Deloder is run, it does the following:

  1. Creates the mutex, testXserv.
  2. Creates the value:

    messnger   [worm filename]

    in the registry key:


    so that the worm runs when you start Windows.
  3. Copies the following two files, which are carried in the worms resources, to your computer:
    • Psexec.exe: This file is 36,352 bytes and is a legitimate remote process launcher. This file is not malicious. The worm uses it to replicate itself.
    • Inst.exe: This file is 684,562 bytes and is an installer of the Trojan, Backdoor.Dvldr, and is detected as such.

  4. Launches multiple network replication threads. Every thread generates a random IP address. For every address, the worm attempts to:
    • Establish a connection using TCP port 445.
    • Copy the dropped Backdoor.Dvldr installer to the remote unrestricted share as the following files:
      • <random_ip>\C$\Documents and Settings\All Users\Start Menu\Programs\Startup\inst.exe
      • <random_ip>\C\WINDOWS\Start Menu\Programs\Startup\inst.exe
      • <random_ip>\C$\Documents and Settings\All Users\Start Menu\Programs\Startup\inst.exe

  5. Inventories network resources and attempts to make a connection to each of them. If the shared resource is password-protected, then the worm attempts to connect to it using a brute-force attack. The worm uses an internal hard-coded list of various passwords that might have been used to restrict the shares, such as "admin," "pass," "12345," and so on.
  6. Attempts to copy and run both itself and Backdoor.Dvldr, by using the legitimate remote process launcher.
  7. Attempts to delete the following default shares (This action is not considered permanent, as the shares will be restored when you restart the computer):
    • E$
    • IPC$
    • ADMIN$
    • F$
    • D$
    • C$
    Symantec ManHunt
    To specifically detect this threat as W32.HLLW.Deloder, Symantec recommends that users of the Symantec ManHunt product activate the HYBRID MODE function and apply the following custom rule:

    *******************start file********************

    alert tcp any any -> any any (msg:"W32.HLLW.Deloder infection"; content: "|59 49 39 E0 C3 1D D3 4D D8 F2 61 73 73 6B 47 69 DA B5 BC 05 3A F0 E4 C7 98 76 CB B4 37 A4 39 4A|";)


    This rule will trigger on successful penetration attacks made by the worm. Please note that this signature was not designed to detect unsuccessful attacks made by the worm.

    For more information on how to create custom signatures, refer to the "Symantec ManHunt Administrative Guide: Appendix A Custom Signatures for HYBRID Mode."


    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.


    The following 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. Run a full system scan and delete all the files detected as W32.HLLW.Deloder or Backdoor.Dvldr.
    3. Delete the value that was added to the registry.
    For specific details on each of these steps, 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 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 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.Deloder or Backdoor.Dvldr, click Delete.

    3. Deleting the value 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

      Then click OK. (The Registry Editor opens.)
    3. Navigate to the key:

    4. In the right pane, delete the value:

      messnger   [worm filename]
    5. Exit the Registry Editor.

    Writeup By: Douglas Knowles