W32.HLLW.Discoball

SUMMARY

W32.HLLW.Discoball is a worm that spreads through network shares. A sign of a possible infection is the existence of Mdbole.exe, Seg32.exe, or Wins.exe.

Protection

• Virus Definitions (LiveUpdate™ Weekly) February 12, 2003
• Virus Definitions (Intelligent Updater) February 11, 2003

Threat Assessment

Wild

• Wild Level: Low
• Number of Infections: 0 - 49
• Number of Sites: 0 - 2
• Geographical Distribution: Low
• Threat Containment: Easy
• Removal: Moderate

Damage

• Damage Level: Low

Distribution

• Distribution Level: Medium
• Shared Drives: Copies itself to windows or winnt folder on all the network shares as MDBOLE.exe

TECHNICAL DETAILS

When W32.HLLW.Discoball runs, it does the following:

1. Copies itself as:
   • %Windir%Mdbole.exe
   • %System%Seg32.exe
   • %System%Wins.exe
     
     NOTES:
     • %Windir% is a variable. The worm locates the Windows installation folder and copies itself to that location. By default, this is C:Windows or C:Winnt.
     • %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:WindowsSystem (Windows 95/98/Me), C:WinntSystem32 (Windows NT/2000), or C:WindowsSystem32 (Windows XP).
       
       
2. Creates the file, %System%Int13ext.vxd.
   
3. Changes the (Default) value in these registry keys:
   
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESoftwareMicrosoftWindows
   CurrentVersionRunOnce
   
   to:
   
   %system%wins.exe
   
   so that the worm runs every time you start Windows.
   
4. Changes the (Default) value of the registry key:
   
   HKEY_CLASS_ROOTexefileshellopencommand
   
   to:
   
   %system%seg32.exe "%1" %*
   
   so that the worm runs every time you run a .exe file.
   
5. Creates the registry key:
   
   HKEY_LOCAL_MACHINESoftwareCLASSESSoftwareMicrosoftWindows
   CurrentVersionRunServices
   
   and sets the (Default) value in this registry key to:
   
   %system%WINS.EXE
   
6. Adds the following text:
   
   run=MDBOLE.EXE
   
   to the [windows] section of the C:WindowsWin.ini file, so that the worm runs every time you start Windows 9598Me.
   
7. Adds the text:
   
   shell=Explorer.exe MDBOLE.EXE
   
   to the [boot] section of the C:WindowsSystem.ini file, so that the worm runs every time you start Windows 9598Me.
   
8. Attempts to use its own SMTP engine to send an email message to a predefined address.
   
9. Inventories all the shared drives.
   
10. Copies itself to the C:Windows or C:Winnt folders as Mdbole.exe, if these folders are found on any shares.
    
11. Adds the text, described in items 6 and 7, to the Win.ini and System.ini files on the remote (shared) computers.

Recommendations

Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":

• Turn off and remove unneeded services. By default, many operating systems install auxiliary services that are not critical, such as an FTP server, telnet, and a Web server. These services are avenues of attack. If they are removed, blended threats have less avenues of attack and you have fewer services to maintain through patch updates.
• If a blended 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 (for example, all Windows-based computers should have the current Service Pack installed.). Additionally, please apply any security updates that are mentioned in this writeup, in trusted Security Bulletins, or on vendor Web sites.
• 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.
• Configure your email server to block or remove email that contains file attachments that are commonly used to spread viruses, such as .vbs, .bat, .exe, .pif and .scr files.
• Isolate infected computers quickly to prevent further compromising your organization. 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.

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. Run a full system scan and delete all the files detected as W32.HLLW.Discoball. Delete the C:\%system%Int13ext.vxd file.
3. Reverse the changes that the worm made to the registry.
4. Remove the lines that the worm added to the Win.ini and System.ini files (Windows 95/98/Me only).

For specific details on each of these sections, read the following instructions.

NOTES:

• If the worm has not yet run—that is, the worm file was copied to your computer but has not run—you should be able to follow the instructions in sections 1 and 2, which detect and remove this file. (If the worm has run, in most cases you will not be able to perform these steps, as the modifications that the worm made will prevent you from doing so.)
• If the worm has run, first follow the instructions in section 3 (and section 4, if you are running Windows 95/98/Me). Then follow the steps in sections 1 and 2.

1. Updating the virus definitions

Symantec Security Response fully tests all 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.
   • For Norton AntiVirus consumer products: Read the document, "How to configure Norton AntiVirus to scan all files."
   • For Symantec AntiVirus Enterprise products: Read the document, "How to verify that a Symantec Corporate antivirus product is set to scan All Files."
2. Run a full system scan.
3. If any files are detected as infected with W32.HLLW.Discoball, click Delete.

3. Reversing the changes that the worm made to 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.

Because the worm modified the registry so that you cannot run the .exe files, first make a copy of the Registry Editor as a file with the .com extension, and then run the file.

1. Do one of the following, depending on which version of Windows you are running:
   • Windows 95/98 users:
     1. Click Start.
     2. Point to Programs.
     3. Click the MS-DOS Prompt. (A DOS window opens at the C:Windows prompt.) Proceed to step b of this section.
   • Windows Me users:
     1. Click Start.
     2. Point to Programs.
     3. Point to Accessories.
     4. Click the MS-DOS Prompt. (A DOS window opens at the C:Windows prompt.) Proceed to step b of this section.
   • Windows NT/2000 users:
     1. Click Start, and then click Run.
     2. Type command, and then press Enter. (A DOS window opens.)
     3. Type cd winnt, and then press Enter.
     4. Go to step b of this section.
   • Windows XP users:
     1. Click Start, and then click Run.
     2. Type command, and then press Enter. (A DOS window opens.)
     3. Type the following commands (pressing Enter after typing each one):
        
        cd
        cd windows
        
     4. Proceed to step b of this section.
        
        
2. Type the following:
   
   copy regedit.exe regedit.com
   
   and then press Enter.
   
3. Type the following:
   
   start regedit.com
   
   and then press Enter. (The Registry Editor will open in front of the DOS window.)
   
   After you finish editing the registry, exit the Registry Editor, and then exit the DOS window.
   
4. Before you continue, 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. For instructions, read the document, "How to make a backup of the Windows registry."
   
5. Navigate to and select the key: HKEY_LOCAL_MACHINESoftwareClassesexefileshellopencommand.
   
   NOTE: The HKEY_LOCAL_MACHINESoftwareClasses key contains many subkey entries that refer to other file extensions. One of these file extensions is .exe. Changing this extension can prevent any files ending with an .exe extension from running. Make sure that you completely browse through this path until you reach the command subkey.
   
   Modify the HKEY_LOCAL_MACHINESoftwareClassesexefileshellopencommand subkey, as shown:
   
   <<=== NOTE: Modify this key.
   
6. In the right pane, double-click the (Default) value.
   
7. Delete the current value data, and then type: "%1" %* (That is, type the characters: quote-percent-one-quote-space-percent-asterisk).
   
   NOTES:
   • In Windows 95/98/Me/NT, the Registry Editor automatically encloses the value within quotation marks. When you click OK, the (Default) value should look exactly like this:
     
     ""%1" %*"  
     
   • In Windows 2000/XP, the additional quotation marks will not appear. When you click OK, the (Default) value should look exactly like this:
     
     "%1" %*
     
   • Make sure that you completely delete all the value data in the command key before typing the correct data. If you leave a space at the beginning of the entry, any attempt to run the program files will result in the error message, "Windows cannot find .exe." If this occurs, restart the entire process from the beginning of this document, and make sure that you completely remove the current value data.
     
     
8. Navigate to each of the following keys:
   
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun
   HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows
   CurrentVersionRunOnce
   
9. For each one, in the right pane, double-click: [Default]
   
10. Delete the text from the Value data box, and then click OK.
    
11. Navigate to and delete the key:
    
    HKEY_LOCAL_MACHINESOFTWARECLASSESSoftwareMicrosoftWindows
    
12. Exit the Registry Editor.

4. Removing the lines from the Win.ini and System.ini files (Windows 95/98/Me only)
The steps that you follow depend on the version of Windows that you are running:

• 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 Win.ini file that you need to edit. If this backup copy exists, it will be in the C:WindowsRecent folder. Symantec recommends that you delete this file before continuing with the steps in this section. To do this, follow these steps:
  1. Start Windows Explorer.
  2. Browse to and select the C:WindowsRecent folder.
  3. In the right pane, select the Win.ini file and System.ini files, and then delete them. The Win.ini and the System.ini files will be regenerated when you save your changes to them in steps f and l.
     
     

1. Click Start, and then click Run.
2. Type the following, and then click OK.
   
   edit c:windowssystem.ini
   
   (The MS-DOS Editor opens.)
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
3. In the [boot] section of the file, look for a line that is similar to the following:
   
   shell=Explorer.exe MDBOLE.EXE
   
4. If this line exists, delete everything to the right of Explorer.exe
   
   When you are done, it should look like:
   
   shell=Explorer.exe
   
5. Click File, and then click Save.
6. Click File, and then click Exit.
7. Click Start, and then click Run.
8. Type the following, and then click OK.
   
   edit c:windowswin.ini
   
   (The MS-DOS Editor opens.)
   
   NOTE: If Windows is installed in a different location, make the appropriate path substitution.
   
9. In the [windows] section of the file, look for a line similar to the following:
   
   run=MDBOLE.EXE
   
10. Delete the entire line if you find it.
11. Click File, and then click Save.
12. Click File, and then click Exit.