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Discovered: July 08, 2002
Updated: February 13, 2007 11:39:32 AM
Also Known As: W32/Ladex.worm [McAfee], Worm.Win32.Ladex.a [KAV], Worm.Win32.Ladex.b [KAV], WORM_LADEX.A [Trend], W32/Ladex-A [Sophos], W32/Ladex-B [Sophos], Win32.Ladex [CA]
Type: Worm
Systems Affected: Microsoft IIS, Windows

W32.Dalbug.Worm will only replicate under NT/2000/XP systems. It spreads by attacking computers that have open user accounts and shares, installing itself remotely as a service on the victim's computer.

NOTE: Definitions dated prior to July 9, 2002 will detect this as WNT.YdalBug.Worm.

Definitions dated prior to July 9, 2002 will detect this as WNT.YdalBug.Worm.

Antivirus Protection Dates

  • Initial Rapid Release version July 08, 2002
  • Latest Rapid Release version March 23, 2017 revision 037
  • Initial Daily Certified version July 08, 2002
  • Latest Daily Certified version March 23, 2017 revision 041
  • Initial Weekly Certified release date July 08, 2002

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

Technical Description

When breaking into a remote computer, W32.Dalbug.Worm attempts to open the computer's Service Control Manager. If successful, it will install itself on the remote computer as a service. The service will have the following attributes:

  • Service name: NtLmHosts
  • Display name: TCP/IP NetBIOS Provider
  • Description: Provides NetBIOS over TCP/IP (NetBT) service support for NetBIOS name resolution.
  • Path: %windir%\System32\lmhsvc.exe

W32.Dalbug.Worm then copies itself as %windir%\System32\lmhsvc.exe, so that the worm is run each time that you restart the computer.

Once it is running, W32.Dalbug.Worm inserts and executes these files:
  • %windir%\Smss.exe
  • %windir%\Csrss.exe

NOTE: %windir% is a variable. It is the folder where Windows is installed. By default, this is C:\Winnt on Windows NT/2000 systems or C:\Windows on Windows XP systems.

It also inserts the file %windir%\System32\Lady.exe. This is a non-malicious joke program that is executed by Smss.exe and Csrss.exe once they are running.

NOTE: The files Smss.exe and Csrss.exe have the same file names as two system files that reside in the %windir%\System32 folder. If you delete these files manually, make sure that you delete the copies that are in the home folder and not the ones in the System32 folder.

During execution, the Smss.exe and Csrss.exe files keep the service running, and checking every three seconds to make sure that it is still running. If you attempt to change or disable the service, it will immediately reinstall it. After 5 minutes of execution time, they activate the Lady.exe program , which will display a few flies crawling across the screen.

During its execution W32.Dalbug.Worm will periodically (every 10 seconds) also add the following registry values:

Smss.exe       %windir%\smss.exe
Csrss.exe      %windir%\csrss.exe

to the registry key


In addition, it tries to kill the Regedit.exe process if it is activated.

Smss.exe and Csrss.exe also try to create the these registry values, however if they detect that Regedit.exe is running, they will delete them (instead of creating them).

Finally, Smss.exe and Csrss.exe will also copy the worm to the following files:



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.


NOTE: These instructions are for all current and recent Symantec antivirus products, including the Symantec AntiVirus and Norton AntiVirus product lines.

Due to the low timer intervals, it is extremely difficult to shut down this worm. However, you must end the processes that are started by the worm before you can remove it. Once the processes have been disabled, update the virus definitions, run a full system scan, and delete all files that are detected as W32.Dalbug.Worm. For details on how to do this, read the following instructions.

To scan for and delete the infected files:

  1. End the processes that were started by the worm.
  2. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      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.
  3. Start your Symantec antivirus software and make sure that it is configured to scan all files.
  4. Run a full system scan.
  5. If any files are detected as infected by W32.Dalbug.Worm, click Delete.

Writeup By: Atli Gudmundsson