Discovered: May 31, 2003
Updated: February 13, 2007 12:01:51 PM
Also Known As: W32/Sobig.c@MM [McAfee], Win32/Sobig.C [ESET], Sobig.C [F-Secure], I-Worm.Sobig.c [KAV], WORM_SOBIG.C [Trend], Win32.Sobig.C [CA], W32/Sobig-C [Sophos]
Type: Worm
Systems Affected: Windows

NOTE : As of June 13, 2003, due to a decreased rate of submissions, Symantec Security Response has downgraded this threat from Category 3 to Category 2.

W32.Sobig.C@mm is a mass-mailing worm that sends itself to all the email addresses that it finds in the files with the following extensions:

  • .wab
  • .dbx
  • .htm
  • .html
  • .eml
  • .txt

The email falsely purports that Microsoft sent it (

Email Routine Details
The email message has the following characteristics:

From: (NOTE : W32.Sobig.C@mm spoofs this field. It could be any address.)

Subject: The subject line will be one of the following:
  • Re: Movie
  • Re: Submited (004756-3463)
  • Re: 45443-343556
  • Re: Approved
  • Approved
  • Re: Your application
  • Re: Application
Message Body: Please see the attached file.

Attachment: The attachment name will be one of the following:
  • screensaver.scr
  • movie.pif
  • submited.pif
  • 45443.pif
  • documents.pif
  • approved.pif
  • application.pif
  • document.pif

NOTE: The worm de-activates on June 8, 2003, and therefore, the last day on which the worm will spread is June 7, 2003.

Antivirus Protection Dates

  • Initial Rapid Release version June 01, 2003
  • Latest Rapid Release version September 28, 2017 revision 037
  • Initial Daily Certified version June 01, 2003
  • Latest Daily Certified version September 29, 2017 revision 001
  • Initial Weekly Certified release date June 01, 2003

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

Technical Description

When W32.Sobig.C@mm is executed, it performs the following actions:

  1. Copies itself as %Windir%\mscvb32.exe.

    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. Creates the following files:
    • %Windir%\msddr.dll
    • %Windir%\msddr.dat

  3. Adds the value:

    "System MScvb"="%Windir%\mscvb32.exe"

    to the registry key:


    so that W32.Sobig.C@mm runs when you start Windows.

  4. If the operating system is Windows NT/2000/XP, then the worm will also add the value:

    "System MScvb"="%Windir%\mscvb32.exe"

    to the registry key:


  5. Counts the Network Resources and copies itself to the following folders:
    • Windows\All Users\Start Menu\Programs\StartUp
    • Documents and Settings\All Users\Start Menu\Programs\Startup

  6. Attempts to download data from four different GeoCities Web pages.

W32.SobigC@mm is also network-aware. It counts the network resources and copies itself to the following folders on other computers to which it has access:
  • Windows\All Users\Start Menu\Programs\StartUp
  • Documents and Settings\All Users\Start Menu\Programs\Startup


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.


Removal using the W32.Sobig.C Removal Tool
Symantec Security Response has created a tool to remove W32.Sobig.C@mm, which is the easiest way to remove this threat.

Manual Removal
As an alternative to using the removal tool, you can manually remove this threat.

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. Do one of the following:
    • Windows 95/98/Me: Restart the computer in Safe mode.
    • Windows NT/2000/XP: End the Trojan process.
  3. Run a full system scan and delete all the files detected as W32.Sobig.C@mm.
  4. Find and delete the files using the Windows Find or Search utility.
  5. Delete the values that were 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: Read "How to update virus definition files using the Intelligent Updater" for detailed instructions.

2. Restarting the computer in Safe mode or ending the Trojan process
    Windows 95/98/Me
    Restart the computer in Safe mode. All the Windows 32-bit operating systems, except for Windows NT, can be restarted in Safe mode. For instructions, read the document, "How to start the computer in Safe Mode."

    Windows NT/2000/XP
    To end the Trojan 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 Mscvb32.exe.
    6. If you find the file, click it, and then click End Process.
    7. Exit the Task Manager.

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.Sobig.C@mm, click Delete.

4. Finding and deleting the files

Follow the instructions for your operating system:
  • Windows 95/98/Me/NT/2000
    1. Click Start, point to Find or Search, and then click Files or Folders.
    2. Make sure that "Look in" is set to (C:) and that "Include subfolders" is checked.
    3. In the "Named" or "Search for..." box, type, or copy and paste, the filenames:

      msddr.dll msddr.dat

    4. Click Find Now or Search Now.
    5. Delete the displayed files.

  • Windows XP
    1. Click Start, and then click Search.
    2. Click All files and folders.
    3. In the "All or part of the file name" box, type, or copy and paste, the filenames:

      msddr.dll msddr.dat

    4. Verify that "Look in" is set to "Local Hard Drives" or to (C:).
    5. Click "More advanced options."
    6. Check "Search system folders."
    7. Check "Search subfolders."
    8. Click Search.
    9. Delete the displayed files.

5. Deleting the values from the registry

CAUTION : 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:

    "System MScvb"="%Windir%\mscvb32.exe"

  5. If the operating system is Windows NT/2000/XP, navigate to the key:


  6. In the right pane, delete the value:

    "System MScvb"="%Windir%\mscvb32.exe"

  7. Exit the Registry Editor.

Writeup By: Douglas Knowles