Threat Explorer

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13 April 2002
13 February 2007
Also Known As:
VBS/Nemite, Exploit.Applet.ActiveXComponen

VBS.Moon@mm is a VBScript threat which is similar to VBS.Loding.A@mm ; it makes use of JS.Exception.Exploit to run its instructions to distribute itself to others using Microsoft Outlook and mIRC. The propagation is a link to a Web site, which downloads the mass-mailing script and executes it.

Antivirus Protection Dates

  • Initial Rapid Release version 15 April 2002
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 15 April 2002
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 17 April 2002
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

This VBScript threat may arrive by email in a simple form. The email message is composed in HTML format and uses an Iframe exploit to open your Web browser to a particular Web page within the http:/ / domain. That Web page runs an HTML script, which downloads a .vbs file to your computer.

Depending on the variant of this script--there are three known variants--the newly created .vbs file will check one of the following registry entries to see whether a marker value of "1" has been set:

A variant:  HKEY_CURRENT_USER\software\moon\explorerb
B variant:  HKEY_CURRENT_USER\software\moon\explorerx
C variant:  HKEY_CURRENT_USER\software\moon\explorer98

If the script does not find the marker value, it assumes that the host system has not been infected, and it does the following:
  1. It copies itself to the \Windows folder as Syashin#.vbs

    NOTE: This file name will vary depending on the variant of the worm. The # could be any number or character.
  2. It adds the value

    explorer     \Windows\Syashin#.vbs

    to the registry key


    This cause the file that it copied in step 1 to run when you start Windows.
  3. Next, it attempts to send itself using Microsoft Outlook. It uses code which slightly resembles that of VBS.LoveLetter. The email is composed in HTML format and is sent only if the following registry entry is not set to "1":


    The format of the email message is as follows:

    Subject: Hi
    Message (in HTML): KONO SYASHIN MITE NE !!!!<Iframe html tag **URL Deleted**>
    Attachment: Syashin#.vbs
  4. The script then searches for standard folders that contain mIRC chat configuration files; if it find such files, it overwrites the existing Script.ini file in an effort to send a copy of the script to others.
  5. The script then sets the Internet Explorer home page to a now defunct Web page in the http:/ / domain.


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.

To remove this Trojan:
  1. Update the virus definitions, run a full system scan, and delete all files that are detected as VBS.Moon@mm
  2. Delete the value

    explorer     \Windows\Syashin#.vbs

    from the registry key

  3. Reset the Internet Explore home page.

For details on how to do this, read the following instructions.

To scan with Norton AntiVirus and delete the Trojan files:
  1. Obtain the most recent virus definitions. There are two ways to do this:
    • Run LiveUpdate. LiveUpdate is the easiest way to obtain virus definitions. These virus definitions have undergone full quality assurance testing by Symantec Security Response and are posted to the LiveUpdate servers one time each week (usually Wednesdays) unless there is a major virus outbreak. To determine whether definitions for this threat are available by LiveUpdate, look at the Virus Definitions (LiveUpdate) line at the top of this write-up.
    • Download the definitions using the Intelligent Updater. Intelligent Updater virus definitions have undergone full quality assurance testing by Symantec Security Response. They are posted on U.S. business days (Monday through Friday). They must be downloaded from the Symantec Security Response Web site and installed manually. To determine whether definitions for this threat are available by the Intelligent Updater, look at the Virus Definitions (Intelligent Updater) line at the top of this write-up.

      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. Start Norton AntiVirus (NAV), and make sure that NAV is configured to scan all files.
  3. Run a full system scan.
  4. Delete all files that are detected as VBS.Moon@mm. Replace the deleted Script.ini file from a clean backup or reinstall mIRC.

To remove the value from 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 only the keys that are specified. Read the document How to make a backup of the Windows registry for instructions.
  1. Click Start, and click Run. The Run dialog box appears.
  2. Type regedit and then click OK. The Registry Editor opens.
  3. Navigate to the following key:

  4. In the right pane, delete the following value:

    explorer     \Windows\Syashin#.vbs
  5. Click Registry, and click Exit.

To reset the Internet Explorer home page:
  1. Start Microsoft Internet Explorer.
  2. Connect to the Internet, and go to the page that you want to set as your home page.
  3. Click Tools, and then click Internet Options.
  4. In the Home page section of the General tab, click Use Current, and then click OK.

Writeup By: Patrick Nolan