Threat Explorer

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VBS.Clyon@mm

VBS.Clyon@mm

Discovered:
21 February 2003
Updated:
13 February 2007
Systems Affected:
Windows

The Visual Basic (VB) Script, VBS.Clyon@mm, is a mass-mailing worm that uses Microsoft Outlook to send itself to all the contacts in Outlook Address Book. The email has the following characteristics:

Subject:  Saludos
Message:
Hola:
Aquí le adjunto mi Curriculum Vitae... Gracias.
Attachment: Iesrack.vbs

NOTE: Definitions dated prior to February 24, 2003 may detect this threat as Bloodhound.VBS.Worm.

Antivirus Protection Dates

  • Initial Rapid Release version 24 February 2003
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 24 February 2003
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 24 February 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When VBS.Clyon@mm runs, it does the following:
  1. Copies itself as C:\Windows\Help\IESRACK.vbs.
  2. Adds the value:

    TavoScript wscript.exe C:\Windows\Help\IESRACK.vbs

    to the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
  3. Attempts to copy itself to a floppy disk using one of the following file names:
    • Juego.exe.vbs
    • Rackcrack.exe.vbs
    • Wd19.tmp.vbs
    • Sexo.jpg.vbs
    • Leeme.txt.vbs
    • Sunat.xls.vbs
    • Planilla general.xls.vbs
    • Matricula de alumnos.xls.vbs
    • Importante.txt.vbs
    • Britney spears.wav.vbs
    • Analisis exaustivo en el lobulo central del cerebro.doc.vbs
    • Aviso.doc.vbs
    • Caratula.cdr.vbs
    • Estado de cuentas.doc.vbs
    • Inventario de los.doc.vbs
    • Solicitud.doc.vbs
    • Relación.doc.vbs
    • Estimados señores.doc.vbs
    • Lista de cumpleaños.doc.vbs
    • Niños de 2 años.doc.vbs

  4. Checks for the Value data of the value, correo, in the registry key:

    HKEY_CURRENT_USER\software\TavoScript
  5. If the registry key does not exist, or the value data is not 1, the worm uses Microsoft Outlook to send itself to all the contacts in the Microsoft Outlook Address Book. The email has the following characteristics:

    Subject: Saludos
    Message:
    Hola:
    Aquí le adjunto mi Curriculum Vitae... Gracias.
    Attachment: Iesrack.vbs

    Then the worm creates the registry key:

    HKEY_CURRENT_USER\software\TavoScript

    and adds the following value to this key:

    correo 1
  6. If the current day of the month is the 11th, the worm displays the following message:


  7. If the current date is December 1st, the worm deletes all the files from the folder, C:\misdoc~1.


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.

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 VBS.Clyon@mm.
  3. Delete the values that the worm added to the registry.

For specific details on each of these steps, 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. 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.
  2. Run a full system scan.
  3. If any files are detected as infected with VBS.Clyon@mm, click Delete.

3. Deleting 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 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

    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:

    TavoScript wscript.exe C:\Windows\Help\IESRACK.vbs
  5. Navigate to the key and delete it:

    HKEY_CURRENT_USER\software\TavoScript
  6. Exit the Registry Editor.



Writeup By: Yana Liu