Discovered: January 09, 2003
Updated: February 13, 2007 11:42:13 AM
Also Known As: W32/Sobig [McAfee], WORM_SOBIG.A [Trend], W32/Sobig-A [Sophos], I-Worm.Sobig [KAV], Win32.Sobig [CA]
Type: Worm
Systems Affected: Windows


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

The W32.Sobig.A@mm worm sends itself to all the addresses it finds in the .txt, .eml, .html, .htm, .dbx, and .wab files. The email message has the following characteristics:
From: big@boss.com
Subject: The subject will be one of these:

  • Re: Movies
  • Re: Sample
  • Re: Document
  • Re: Here is that sample

Attachment: The attachment will be one of these:
  • Movie_0074.mpeg.pif
  • Document003.pif
  • Untitled1.pif
  • Sample.pif

Before W32.Sobig.A@mm sends the messages, it sends a message to an address at pagers.icq.com.

The worm also attempts to copy itself to the following folders on all the open network shares:
  • \Windows\All Users\Start Menu\Programs\StartUp
  • Documents and Settings\All Users\Start Menu\Programs\Startup

Note: Symantec Security Response has received reports of W32.Sobig.A@mm downloading and installing the Backdoor Trojan, Backdoor.Lala .

Antivirus Protection Dates

  • Initial Rapid Release version January 10, 2003
  • Latest Rapid Release version August 08, 2016 revision 023
  • Initial Daily Certified version January 10, 2003
  • Latest Daily Certified version August 09, 2016 revision 001
  • Initial Weekly Certified release date January 10, 2003

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

Writeup By: Douglas Knowles

Discovered: January 09, 2003
Updated: February 13, 2007 11:42:13 AM
Also Known As: W32/Sobig [McAfee], WORM_SOBIG.A [Trend], W32/Sobig-A [Sophos], I-Worm.Sobig [KAV], Win32.Sobig [CA]
Type: Worm
Systems Affected: Windows


When W32.Sobig.A@mm is executed, it does the following:

  1. Copies itself as %Windir%\Winmgm32.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 a %Windir%\Winmgm32.exe process, with the parameter of "start." The Winmgm32.exe process does the following:
    1. Creates a Mutex with the name Worm.X.
    2. Creates a thread to send a message to an address on pagers.icq.com.
    3. Creates a thread to download the content from a specific Web site to the file %Windir%\dwn.dat. Then, the worm executes the content that it downloaded.
    4. Creates a thread to search the network for all the open shares, as well as to copy itself to the following folders on those particular shares:
      • Windows\All Users\Start Menu\Programs\StartUp
      • Documents and Settings\All Users\Start Menu\Programs\Startup
    5. Creates a thread to send email to all the addresses it finds in the files with the following extensions:
      • .txt
      • .eml
      • .html
      • .htm
      • .dbx
      • .wab
    6. Configures itself to start when you start Windows, by adding the value:

      WindowsMGM %Windir%\Winmgm32.exe

      to the registry key:

      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run


Email routine details
The messages sent during the email routine have these characteristics:
From: big@boss.com
Subject: The subject will be one of these:
    • Re: Movies
    • Re: Sample
    • Re: Document
    • Re: Here is that sample
Attachment: The attachment will be one of these:
    • Movie_0074.mpeg.pif
    • Document003.pif
    • Untitled1.pif
    • Sample.pif
The worm stores the addresses to which it sends the email messages in the file %Windir%\Sntmls.dat.

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: Douglas Knowles

Discovered: January 09, 2003
Updated: February 13, 2007 11:42:13 AM
Also Known As: W32/Sobig [McAfee], WORM_SOBIG.A [Trend], W32/Sobig-A [Sophos], I-Worm.Sobig [KAV], Win32.Sobig [CA]
Type: Worm
Systems Affected: Windows



Removal tool
Symantec has provided a tool to remove infections of W32.Sobig.A@mm. Click here to obtain the tool. Try this removal tool first, as it is the easiest way to remove the threat.

Manual removal

These 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. Restart the computer or end the Worm process, by performing the following:
    • Windows 95/98/Me: Restart the computer in Safe mode.
    • Windows NT/2000/XP: End the Worm process.
  3. Run a full system scan and delete all the files detected as W32.Sobig.A@mm.
  4. Reverse the changes that the Worm made to the registry.
  5. Find and delete the data files created by the worm.
For specific details on each of these procedures, 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 the 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), in the "Protection" section, at the top of this writeup.
  • 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), in the "Protection" section, at the top of this writeup.

    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. 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 Winmgm32.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 4. Reversing the changes made to 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, and then click OK. (The Registry Editor opens.)
  3. Navigate to the key:

    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run
  4. In the right pane, delete the value:

    WindowsMGM %windir%\winmgm32.exe
  5. Exit the Registry Editor.

5. Finding and deleting the data 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 file names: dwn.dat sntmls.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 file names: dwn.dat sntmls.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.

Writeup By: Douglas Knowles