Discovered: August 29, 2005
Updated: February 13, 2007 12:43:46 PM
Type: Worm
Systems Affected: Windows

W32.Bobax.AH@mm is a mass-mailing worm that attempts to use the compromised computer as a covert proxy. The worm spreads by exploiting the Microsoft Windows Plug and Play Buffer Overflow Vulnerability (as described in Microsoft Security Bulletin MS05-03 9 ) and by sending a copy of itself to email addresses gathered.

Antivirus Protection Dates

  • Initial Rapid Release version August 30, 2005
  • Latest Rapid Release version September 28, 2010 revision 054
  • Initial Daily Certified version August 30, 2005
  • Latest Daily Certified version September 28, 2010 revision 036
  • Initial Weekly Certified release date August 31, 2005

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

Writeup By: Rodney Andres

Discovered: August 29, 2005
Updated: February 13, 2007 12:43:46 PM
Type: Worm
Systems Affected: Windows

When W32.Bobax.AH@mm is executed, it performs the following actions:

  1. Copies itself as %System%\[RANDOM FILE NAME].exe.

    Note: %System% is a variable that refers to the System folder. By default this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

  2. Adds the value:

    "[RANDOM VALUE]" = "%System%\[RANDOM FILE NAME].exe"

    to the registry subkey:


    so that it runs every time Windows starts.

  3. Creates the following DLL file:


    Note: %Temp% is a variable that refers to the Windows temporary folder. By default, this is C:\Windows\TEMP (Windows 95/98/Me/XP) or C:\WINNT\Temp (Windows NT/2000).

  4. Downloads files to %Windir%\[RANDOM STRING].tmp from the following URLs:

    • [http://][REMOVED]pub/ICQ_Win95_98_NT4/ICQ_4/Lite_Edition/icq4_setup.exe
    • [http://][REMOVED]pub/ Setup 1.0.exe
    • [http://][REMOVED]aim/win95/Install_AIM.exe

      Note: %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows or C:\Winnt.

  5. Deletes the following files:


  6. Disables any windows that contain the string "processes", or any that have the windows class "syslistview32". This will result in the "Processes" tab of the Task Manager window being disabled.

  7. Modifies the following registry entries :

    "AntiVirusDisableNotify" = "1"
    "AntiVirusOverride" = "1"
    "FirewallDisableNotify" = "1"
    "FirewallOverride" = "1"
    "UpdatesDisableNotify" = "1"

    in the registry subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center

    to lower security settings.

  8. Modifies the value:

    "Start" = "4"

    in the registry subkeys:


    to disable the SharedAccess service.

  9. Disables the Windows firewall.

  10. Injects the file %Temp%\Was*.tmp into all processes, which are prepended with the following strings:

    • expl
    • Winl
    • serv

      This includes the following Windows system processes:

    • explorer.exe
    • Winlogon.exe
    • services.exe

  11. Attempts to use the compromised computer as a covert proxy.

  12. Gathers email addresses from the Windows Address Book, Windows Messenger contact list, and files with one of the following extensions:

    • .htm
    • .txt
    • .dbx

  13. Sends a copy of itself to the email addresses gathered using one of the following SMTP servers :


  14. The email may have the following characteristics:

    One of the following:

    • Cool
    • pics
    • funny
    • bush
    • joke
    • secret

      One of the following:

    • Saddam Hussein - Attempted Escape, Shot dead
    • Attached some pics that i found
    • Osama Bin Laden Captured.
    • Attached some pics that i found
    • Testing
    • Secret!
    • Hey,
    • Remember this?
    • Hello,
    • Long time! Check this out!
    • Hey,
    • I was going through my album, and look what I found..
    • Hey,
    • Check this out :-)

      Followed by one of the following messages:

    • ++ Attachment: No Virus found
    • ++ Panda AntiVirus - You are protected
    • ++
    • ++ Attachment: No Virus found
    • ++ Norman AntiVirus - You are protected
    • ++
    • ++ Attachment: No Virus found
    • ++ F-Secure AntiVirus - You are protected
    • ++
    • ++ Attachment: No Virus found
    • ++ Norton AntiVirus - You are protected
    • +++

      A copy of the worm, with one of the following extensions:

    • .pif
    • .scr
    • .exe
    • .zip

  15. Avoids sending itself to email addresses whose domain contains any of the following strings:

    • ogle
    • yaho
    • help
    • admi
    • ter@
    • micr
    • msn.
    • hotm
    • supp
    • yman
    • viru
    • tren
    • secu
    • .mil
    • urhq
    • pand
    • afee
    • soph
    • kasp
    • .gov
    • nort

  16. Attempts to spread to other computers by exploiting the Microsoft Windows Plug and Play Buffer Overflow Vulnerability (as described in Microsoft Security Bulletin MS05-039) on TCP port 445.

  17. Creates a HTTP connection with the host computer on a random port.

  18. Downloads and executes a copy of itself and saves the file with a .gif extension, if a successful connection is made.

  19. Contacts one of the following domains on a remote Web server and sends a unique ID and information about the newly compromised computer as notification of infection:

    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]
    • [http://][REMOVED]

  20. Adds the following text to the hosts file to block access to several security-related Web sites: 

  21. Searches registry values in the following subkey and infects some of the files found:


  22. Searches for and infects .exe files.

  23. Renames original file by appending .tmp to the filename and extension.


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: Rodney Andres

Discovered: August 29, 2005
Updated: February 13, 2007 12:43:46 PM
Type: Worm
Systems Affected: Windows

Removal using the W32.Bobax Removal Tool
Symantec Security Response has developed a removal tool to clean the infections of W32.Bobax.AH@mm. Use this removal tool first, as it is the easiest way to remove this threat.

Manual Removal:

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. Remove all the entries that the risk added to the hosts file.
  3. Update the virus definitions.
  4. Run a full system scan and repair or delete all the files detected.
  5. Delete any values added to the registry.
  6. Reenable the SharedAccess service (Windows 2000/XP only)
  7. Restore the Windows Security Center.
For specific details on each of these steps, read the following instructions.

1. To disable 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:
When you are completely finished with the removal procedure and are satisfied that the threat has been removed, reenable 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. To remove all the entries that the risk added to the hosts file
  1. Navigate to the following location:

    • Windows 95/98/Me:
    • Windows NT/2000/XP:

    • The location of the hosts file may vary and some computers may not have this file. There may also be multiple copies of this file in different locations. If the file is not located in these folders, search your disk drives for the hosts file, and then complete the following steps for each instance found.
    • %Windir% is a variable that refers to the Windows installation folder. By default, this is C:\Windows (Windows 95/98/Me/XP) or C:\Winnt (Windows NT/2000).

  2. Double-click the hosts file.
  3. If necessary, deselect the "Always use this program to open this program" check box.
  4. Scroll through the list of programs and double-click Notepad.
  5. When the file opens, delete all the entries added by the risk. (See the Technical Details section for a complete list of entries.)
  6. Close Notepad and save your changes when prompted.
3. To update 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 Virus Definitions (LiveUpdate).
  • Downloading the definitions using the Intelligent Updater: The Intelligent Updater virus definitions are posted daily. 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 Virus Definitions (Intelligent Updater).

    The latest Intelligent Updater virus definitions can be obtained here: Intelligent Updater virus definitions. For detailed instructions read the document: How to update virus definition files using the Intelligent Updater.

4. To scan for and repair the infected files
  1. Start your Symantec antivirus software and make sure that it is configured to scan all the files.
  2. Run a full system scan.
  3. If any files are detected, click Repair (if available). If there is no Repair option, click Delete.

    Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot repair or delete a detected file, you may need to stop the risk from running in order to remove it. To do this, run the scan in Safe mode. For instructions, read the document, How to start the computer in Safe Mode. Once you have restarted in Safe mode, run the scan again.

    After the files are repaired or deleted, restart the computer in Normal mode and proceed with the next section.

    Warning messages may be displayed when the computer is restarted, since the threat may not be fully removed at this point. You can ignore these messages and click OK. These messages will not appear when the computer is restarted after the removal instructions have been fully completed. The messages displayed may be similar to the following:

    Title: [FILE PATH]
    Message body: Windows cannot find [FILE NAME]. Make sure you typed the name correctly, and then try again. To search for a file, click the Start button, and then click Search.

5. To delete the value from the registry
Important: 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 subkeys only. For instructions refer to the document: How to make a backup of the Windows registry.
  1. Click Start > Run.
  2. Type regedit
  3. Click OK.

    Note: If the registry editor fails to open the threat may have modified the registry to prevent access to the registry editor. Security Response has developed a tool to resolve this problem. Download and run this tool, and then continue with the removal.

  4. Navigate to the subkey:


  5. In the right pane, delete the value:

    "[RANDOM VALUE]" = "%System%\[RANDOM FILE NAME].exe"

  6. Navigate to the subkey:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Security Center

  7. In the right pane restore the following entries to their original values:

    "AntiVirusDisableNotify" = "1"
    "AntiVirusOverride" = "1"
    "FirewallDisableNotify" = "1"
    "FirewallOverride" = "1"
    "UpdatesDisableNotify" = "1"

  8. Exit the Registry Editor.

6. To reenable the SharedAccess service (Windows 2000/XP only)
The SharedAccess service is responsible for maintaining Internet Connection Sharing and the Windows Firewall/Internet Connection Firewall applications in Windows. (The presence and names of these applications vary depending on the operating system and service pack you are using.) To protect your computer and maintain network functionality, re-enable this service if you are using any of these programs.

Windows XP Service Pack 2
If you are running Windows XP with Service Pack 2 and are using the Windows Firewall, the operating system will alert you when the SharedAccess service is stopped, by displaying an alert balloon saying that your Firewall status is unknown. Perform the following steps to ensure that the Windows Firewall is re-enabled:
  1. Click Start > Control Panel.

  2. Double-click the Security Center.

  3. Ensure that the Firewall security essential is marked ON.

    Note: If the Firewall security essential is marked on, your Windows Firewall is on and you do not need to continue with these steps.

    If the Firewall security essential is not marked on, click the "Recommendations" button.

  4. Under "Recommendations," click Enable Now. A window appears telling you that the Windows Firewall was successfully turned on.

  5. Click Close, and then click OK.

  6. Close the Security Center.

Windows 2000 or Windows XP Service Pack 1 or earlier
Complete the following steps to re-enable the SharedAccess service:
  1. Click Start > Run.
  2. Type services.msc

    Then click OK.

  3. Do one of the following:
    • Windows 2000: Under the Name column, locate the "Internet Connection Sharing (ICS)" service and double-click it.
    • Windows XP: Under the Named column, locate the "Internet Connection Firewall (ICF) / Internet Connection Sharing (ICS)" service and double-click it.

  4. Under "Startup Type:", select "Automatic" from the drop-down menu.

  5. Under "Service Status:", click the Start button.

  6. Once the service has completed starting, click OK.

  7. Close the Services window.

7. To restore the Windows Security Center
This risk attempts to disable the features in the Windows Security Center, available in Windows XP Service Pack 2. If you are running Windows XP Service Pack 2 and would like to restore the full functionality of the Windows Security Center, please complete the following steps:

Important: If your computer is connected to a domain, you may not be able to adjust these settings. If so, contact your network administrator for more information.
  1. Click Start > Control Panel.
  2. Double-click the Security Center.
  3. In the right pane, click Windows Firewall. The Windows Firewall appears.
  4. Select On.
  5. Click OK to close the Windows Firewall.
  6. In the left pane of the Security Center, select Change the way Security Center alerts me.
  7. Click Alert Settings.
  8. Select Alert Settings, Firewall, and Virus Protection.
  9. Click OK
  10. Click Automatic Updates.
  11. Select Automatic.
  12. Click OK.
  13. Exit the Security Center.

Writeup By: Rodney Andres