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Discovered: February 10, 2004
Updated: February 13, 2007 12:17:17 PM
Also Known As: W32/Mimail.u@MM [McAfee], Win32.Mimail.U[Computer Associ
Type: Worm
Systems Affected: Windows

W32.Dumaru.AH@mm is a multi-threaded, mass-mailing worm that opens a backdoor, runs a keylogger, and attempts to steal personal information. The worm uses its own SMTP engine to spread to email addresses that it finds in the files on an infected system.

The email has the following characteristics:

From:  random characters@<a domain from an email addresses found on the infected computer>
Subject: Unknown
Attachment: document.zip (The attachment is a zip file that contains the worm executable, myphoto.jpg<56 spaces>.exe.)

The worm is similar to the W32.Dumaru.Y@mm worm and arrives as a dropper.

Antivirus Protection Dates

  • Initial Rapid Release version February 11, 2004
  • Latest Rapid Release version December 01, 2016 revision 025
  • Initial Daily Certified version February 11, 2004
  • Latest Daily Certified version December 02, 2016 revision 001
  • Initial Weekly Certified release date February 11, 2004

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

Technical Description

W32.Dumaru.AH@mm has a polymorphic dropper, which drops and runs the file C:\nload.exe. The dropped file is 28,020 bytes in size and is compressed with FSG. This file contains the worm's email routine.

When nload.exe runs, it does the following:

  1. Creates the file, %Windir%\TEMP\photo.jpg, and launches explorer.exe to load the following image:

    Note: %Windir% is a variable. The worm locates the Windows installation folder (by default, this is C:\Windows or C:\Winnt) and copies itself to that location.

  2. May copy itself as the following:
    • %System%\1111a.exe
    • %System%\1111c.exe

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

  3. May copy itself to the startup folder as 1111b.exe.

  4. Adds a value:


    to the registry key:


    so that the worm runs when Windows starts.

  5. Modifies the value:

    "Shell"="explorer.exe %System%\1111c.exe"

    in the registry key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

    so that the worm runs when Windows NT/2000/XP starts.

  6. Modifies the [boot] section of the system.ini file (Windows 95/98/Me only) as follows:

    shell=explorer.exe %System%\1111c.exe

    so that the worm runs when Windows 95/98/Me starts.

  7. Attempts to download a file named nvidia32.exe from a predetermined Web site. This file is a Backdoor Trojan that logs keystrokes and steals system information from a compromised computer.

  8. Creates the following registry key if the worm successfully downloads nvidia32.exe:


  9. Retrieves email addresses from the files with the following extensions:
    • .htm
    • .wab
    • .html
    • .dbx
    • .tbb
    • .abd

      The email addresses will be saved in the file, %Windir%\1111mail.log.

  10. Creates a file named %Windir%\Temp\Zip.tmp, which contains the worm.

  11. Uses its own SMTP engine to email a .zip file, which contains the worm, to the addresses previously found.

    The email has the following characteristics:

    From: random characters@<a domain from an email addresses found on the infected computer>
    Subject: Unknown
    Message: If you cant see message text from: <some random characters> , read attached file.
    Attachment: document.zip (The attachment is a zip file that contains the worm executable, myphoto.jpg<56 spaces>.exe.)

  12. Launches multiple new threads, each designed for a specific purpose. The threads will do the following:
    • Creates a WindowsHook, so that the worm gains control when certain actions occur on the computer. This thread is designed to steal passwords, and it will log passwords as they are typed into Web forms and programs. They will be saved in the file, 1111k.log.
    • Harvests passwords for a variety of programs; however, it specifically targets those for www.e-gold.com. For any Web form on this site, the worm will begin logging all the keystrokes.
    • Copies certain information from the clipboard into the file, 1111c.log.
    • Opens ports on the system and waits for incoming connections. One thread will listen on TCP port 10000 and another on TCP port 2283.
    • Periodically checks the size of the files it uses for logging stolen information, and when they reach a certain size, the information will be sent to a hard-coded FTP server (See step 13).
    • Run two backdoor threads, allowing an attacker to access the system and gain full control, as well as use an infected computer as a relay.

  13. Retrieves the IP address of the current machine. The worm uses this IP address as the file name it sends to an FTP server.

    For example, if the machine's IP address is A.B.C.D, then the file name will be A.B.C.D.eml. The file contains the following information:

    From: <current user name><address@yandex.ru>
    To: You
    IP address: <the computer's IP address>
    *** System information ***
    Windows version: <OS version>
    Internet Explorer version: <IE version>
    *** Far Manager passwords ***
    *** System information ends ***
    *** Far Manager passwords ***
    <clipboard log>
    *** Protected Storage Data ***
    <protected storage data>
    *** Protected Storage Data ends ***


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. Disable System Restore (Windows Me/XP).
  2. Update the virus definitions.
  3. Do one of the following:
    • Windows 95/98/Me: Restart the computer in Safe mode.
    • Windows NT/2000/XP: End the malicious process.
  4. Run a full system scan and delete all the files detected as W32.Dumaru.AH@mm.
  5. Reverse the changes made to the registry.
  6. Edit the System.ini file (Windows 95/98/Me).
For details on each of these steps, read the following instructions.

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. Restarting the computer in Safe mode or ending the malicious process
    Windows 95/98/Me
    Shut down the computer and turn off the power. Wait for at least 30 seconds, and then restart the computer in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

    Windows NT/2000/XP
    To end the malicious process:
    1. Press Ctrl+Alt+Delete once.
    2. Click Task Manager.
    3. Click the Processes tab.
    4. Double-click the Image Name column header to alphabetically sort the processes.
    5. Scroll through the list and look for "nload.exe."
    6. If you find one of these files, click it, and then click End Process.
    7. Exit the Task Manager.
4. 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.Dumaru.AH@mm, click Delete.

5. Reversing the changes made to the registry

WARNING: 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. 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:


  5. Do one of the following:
    • If you are using Windows 95/98/Me, proceed to step i.
    • If you are using Windows NT/2000/XP, continue with step f.

  6. Navigate to the key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

  7. In the right pane, modify the value:

    "Shell"="explorer.exe %System%1111c.exe"



  8. Exit the Registry Editor.

  9. Restart the computer back into Normal mode. For instructions, read the section on returning to Normal mode in the document, "How to start the computer in Safe Mode."

6. Editing the System.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 System.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 System.ini file and delete it. The System.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\system.ini

    (The MS-DOS Editor opens.)

    NOTE: If Windows is installed in a different location, make the appropriate path substitution.

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

    shell = Explorer.exe %System%\1111c.exe

  5. If this line exists, delete everything to the right of Explorer.exe.

    When you are done, it should look like:

    shell = Explorer.exe

  6. Click File, and then click Save.

  7. Click File, and then click Exit.

Writeup By: Yana Liu