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Discovered: September 01, 2005
Updated: February 13, 2007 12:44:07 PM
Type: Worm
Systems Affected: Windows

W32.Theals.A@mm is a mass-mailing worm that sends itself as password protected .zip file. The worm is also able to spread across the local network by exploiting vulnerabilities and can hide itself using rootkit functionalities. The worm steals confidential information and WebMoney files.

Antivirus Protection Dates

  • Initial Rapid Release version September 02, 2005
  • Latest Rapid Release version May 31, 2016 revision 036
  • Initial Daily Certified version September 02, 2005
  • Latest Daily Certified version June 01, 2016 revision 005
  • Initial Weekly Certified release date September 07, 2005

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

Writeup By: Elia Florio

Discovered: September 01, 2005
Updated: February 13, 2007 12:44:07 PM
Type: Worm
Systems Affected: Windows

When W32.Theals.A@mm is executed, it performs the following actions:

  1. Arrives in an email as a unique file that drops all the other components. The dropper could be an executable file or an .hta file.

  2. Creates and executes the following files:
    • C:\stealth.exe
    • C:\stealth.dcom.exe
    • C:\stealth.ddos.exe
    • C:\stealth.injector.exe
    • C:\stealth.stat.exe
    • C:\stealth.wm.exe
    • C:\stealth.worm.exe
    • C:\stealth.shared.dll
    • C:\stealth.bszip.dll

      Note: The file C:\stealth.bszip.dll is a clean compression library used by the worm. All of the files require the stealth.shared.dll library to work.

  3. Adds the values:

    "stealth.exe" = "C:\stealth.exe"
    "stealth.dcom.exe" = "C:\stealth.dcom.exe"
    "stealth.ddos.exe" = "C:\stealth.ddos.exe"
    "stealth.injector.exe" = "C:\stealth.injector.exe"
    "stealth.stat.exe" = "C:\stealth.stat.exe"
    "stealth.wm.exe" = "C:\stealth.wm.exe"
    "stealth.worm.exe" = "C:\stealth.worm.exe"

    to the registry subkey:


    so that it runs every time Windows starts.

  4. Hides its presence by hooking the following Windows APIs:

    • RegEnumValueA
    • RegEnumValueW
    • FindNextFileA
    • FindNextFileW
    • Process32Next

  5. Works as a rootkit and hides all files, processes, and registry subkeys that begin with the string "stealth".

  6. Generates a random password of 12 digits and writes it as bitmap image in the following file:


  7. Copies the installer using a random file name with a random extension that could be one of the following:

    • .exe
    • .scr
    • .bat

  8. Puts this file into a ZIP archive, which is protected with the random password in the stealth.pass.bmp file:


  9. Searches for the following processes in memory, executing the mass-mailing routine each time they are found:

    • msimn.exe
    • outlook.exe
    • thebat.exe

  10. Injects its malicious code inside these processes, altering the functioning of "ws2_32.send()" API.

  11. Sends itself as an attachment to an email with the following characteristics:

    Message Body:


    Note: The message includes a bitmap image.

    One of the following names:

    • Document.zip
    • Foto.zip
    • Secret.zip
    • PORNO.zip
    • Tetris.zip

  12. Intercepts the following strings and collects them in the file C:\stealth.injector.rpt during the mail spreading process:

    • USER
    • PASS

  13. Gathers the current IP address and generates IP addresses that would reside on a local network A.B.C.X, where X is a number between 1 and 254.

  14. Copies itself to vulnerable computers on the local network by exploiting the Microsoft Windows DCOM RPC Interface Buffer Overrun Vulnerability (described in Microsoft Security Bulletin MS03-026).

  15. Tries to perform a distributed denial of service against the following Web sites, sending randomly generated packets over TCP port 80:

    • kaspersky.com
    • kaspersky.ru

  16. Overwrites the hosts file with the following entries: ad.doubleclick.net ad.fastclick.net ads.fastclick.net ar.atwola.com atdmt.com avp.ch avp.com avp.com avp.ru awaps.net banner.fastclick.net banners.fastclick.net ca.com ca.com click.atdmt.com clicks.atdmt.com customer.symantec.com dispatch.mcafee.com dispatch.mcafee.com download.mcafee.com download.mcafee.com download.mcafee.com download.microsoft.com downloads.microsoft.com downloads1.kaspersky-labs.com downloads1.kaspersky-labs.com downloads1.kaspersky-labs.com/updates downloads2.kaspersky-labs.com downloads3.kaspersky-labs.com downloads4.kaspersky-labs.com downloads-us1.kaspersky-labs.com downloads-us2.kaspersky-labs.com downloads-us3.kaspersky-labs.com engine.awaps.net fastclick.net f-secure.com f-secure.com ftp.avp.ch ftp.downloads2.kaspersky-labs.com ftp.f-secure.com ftp.kasperskylab.ru ftp.sophos.com go.microsoft.com ids.kaspersky-labs.com kaspersky.com kaspersky-labs.com liveupdate.symantec.com liveupdate.symantec.com liveupdate.symantec.com liveupdate.symantecliveupdate.com liveupdate.symantecliveupdate.com localhost mast.mcafee.com mast.mcafee.com mcafee.com mcafee.com media.fastclick.net msdn.microsoft.com my-etrust.com my-etrust.com nai.com nai.com networkassociates.com networkassociates.com office.microsoft.com phx.corporate-ir.net rads.mcafee.com secure.nai.com secure.nai.com securityresponse.symantec.com securityresponse.symantec.com service1.symantec.com sophos.com sophos.com spd.atdmt.com support.microsoft.com symantec.com symantec.com trendmicro.com update.symantec.com update.symantec.com update.symantec.com updates.symantec.com updates.symantec.com updates1.kaspersky-labs.com updates1.kaspersky-labs.com updates2.kaspersky-labs.com updates3.kaspersky-labs.com updates3.kaspersky-labs.com/updates updates4.kaspersky-labs.com updates5.kaspersky-labs.com us.mcafee.com us.mcafee.com vil.nai.com viruslist.com viruslist.ru windowsupdate.microsoft.com www.avp.ch www.avp.com www.avp.com www.avp.ru www.awaps.net www.ca.com www.ca.com www.fastclick.net www.f-secure.com www.f-secure.com www.grisoft.com www.kaspersky.com www.kaspersky.ru www.kaspersky.ru www.kaspersky-labs.com www.mcafee.com www.mcafee.com www.my-etrust.com www.my-etrust.com www.nai.com www.nai.com www.networkassociates.com www.networkassociates.com www.sophos.com www.sophos.com www.symantec.com www.symantec.com www.trendmicro.com www.trendmicro.com www.viruslist.com www.viruslist.ru www3.ca.com

  17. Collects the operating system version and country of the compromised computer and sends it to the following URL:


  18. Periodically scans the process list looking for the webmoney.exe program. If found, the worm collects WebMoney files when they are accessed. The files, reports, and accounts are saved as the following files:

    • C:\stealth.wm.rpt
    • C:\stealth.wm.kvm
    • C:\stealth.wm.pwm
    • C:\stealth.wm

  19. Sends files to a predetermined email address on the mail.ru domain, using smtp.mail.ru as the outgoing email server.


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: Elia Florio

Discovered: September 01, 2005
Updated: February 13, 2007 12:44:07 PM
Type: Worm
Systems Affected: Windows

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 delete all the files detected.
  5. Delete any values added to the registry.
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 delete 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, click Delete.

Important: If you are unable to start your Symantec antivirus product or the product reports that it cannot 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 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 values:

    "stealth.exe" = "C:\stealth.exe"
    "stealth.dcom.exe" = "C:\stealth.dcom.exe"
    "stealth.ddos.exe" = "C:\stealth.ddos.exe"
    "stealth.injector.exe" = "C:\stealth.injector.exe"
    "stealth.stat.exe" = "C:\stealth.stat.exe"
    "stealth.wm.exe" = "C:\stealth.wm.exe"
    "stealth.worm.exe" = "C:\stealth.worm.exe"

  6. Exit the Registry Editor.

Writeup By: Elia Florio