Threat Explorer

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VBS.DLetter@mm

VBS.DLetter@mm

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

VBS.DLetter@mm is a worm written in Visual Basic Script. When executed, the worm attempts to send itself to all the recipients in the Microsoft Outlook address book. The email will have a subject which is randomly chosen from a predetermined list and an attachment with a .mht file extension.

VBS.DLetter@mm also spreads using the IRC, mIRC, and KaZaA-shared folders.

Antivirus Protection Dates

  • Initial Rapid Release version 19 February 2003
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 19 February 2003
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 19 February 2003
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When VBS.DLetter@mm is run, the following events occur:
  1. A .hta (HTML Application) file, which contains the worm as an embedded VBScript, is created by executing the .mht (MHT or MHTML document) file.

    NOTE: The paths and file names of the .hta file and .mht file are the same, except for the file extension.
  2. A copy of the worm will be generated as %System%\DeathLetter.vbe, by executing the previously created .hta file.

    NOTE: %System% is a variable. The worm locates the System folder and copies itself to that location. By default, this is C:\Windows\System (Windows 95/98/Me), C:\Winnt\System32 (Windows NT/2000), or C:\Windows\System32 (Windows XP).

    Then, the worm adds the value:

    "DeathLetter" = "%System%\DeathLetter.vbe"

    to the registry key:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run

    so that the worm runs each time Windows starts.

    If this VBScript worm finds a .mht file in the same directory in which the .hta file is located, and the .mht file has the same file name as the .hta file, then the worm copies the .mht file to the %System% directory as Letter_of_the_Death.mht and ComoHackearUnMail.mht. Then, the worm deletes the .mht file from the directory in which the .hta file is located.
  3. The worm will replicate itself through Microsoft Outlook, by executing the DeathLetter.vbe file. The worm completes this process by performing the following functions:
    1. Attempts to copy the infected file, %System%\Letter_of_the_Death.mht, to the %Tempdir% directory as one of the following files:

      NOTE:
      %Tempdir% is a variable. The worm locates the Temporary folder and copies itself to that location. By default, this is C:\Windows\Temp.
      • MailFile.mht
      • www.ftpfree.mht
      • Microsoft Bulletin 207.mht
      • www.Models.mht
      • www.gmol.mht
      • www.rdA.mht
      • Trivia.mht
      • NoHabrasEsto.mht
      • EnterTvRed.mht
      • Boletin N.205.mht

    2. Creates an email message in HTML format to be sent to everyone in the Microsoft Outlook Address Book, as well as to the hacker's email address, sachiel2015@latinmail.com. The email message sent to the Microsoft Outlook email addresses looks like:

      Subject: randomly selected from the following:
      Mail Delivery Return System
      Invitacion
      Microsoft Internet Explorer
      Models
      Games OnLine
      Buscas Amistad o Amor?
      Adivinanzas y Trivias
      Te Estan Espiando?
      Series, Peliculas, Telenovelas
      Confirmacion de Suscripción

      Body: randomly selected messages
      Attachment: randomly selected .mht files in %tempdir% directory, which is copied from %system%\Letter_of_the_Death.mht.

      The message sent to the hacker looks like the following:
      Subject: VBS/DeathLetter Reportandose
      Body: ProductName, RegisteredOrganization, and RegisteredOwner value in the registry key
      HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion
    3. After sending the email message through Microsoft Outlook, the VBS.DLetter@mm worm adds the values:

      "%Recipients%" = "DMail"

      to the registry key:

      HKEY_CURRENT_USER\Software\Gedzac Labs\VBS.OM\Mail\

      NOTE: %Recipients% is a variable of the email addresses of all the recipients in the Microsoft Outlook Address Book, as well as the hacker's email address, sachiel2015@latinmail.com.
    4. Sends similar email messages through the Microsoft MAPI session, and then adds the values:

      "%recipients%" = "DMail"

      to the registry key:

      HKEY_CURRENT_USER\Software\Gedzac Labs\VBS.XM\Mail\

  4. If the worm is not run as an embedded VBScript in a .mht file or .hta file, then it replicates through the Kazaa-shared folders, IRC and mIRC, by doing the following:
    1. Copies the infected file, %System%\Letter_of_the_Death.mht, to some .mht files in the Kazaa-shared directory, and then adds the values:

      dir0   "012345:%system%\GEDZAC_LABS(P2P)

      DisableSharing  0

      to the registry key:

      HKEY_CURRENT_USER\Software\Kazaa\LocalContent\

      This sets the %System%\GEDZAC_LABS(P2P) folder to be a KaZaA-shared folder.
    2. Adds the values:

      virus_filter  0
      firewall_filter  0

      to the registry key:

      HKEY_CURRENT_USER\Software\KAZAA\ResultsFilter

    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.DLetter@mm.
    3. Reverse the changes that the Trojan made 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) line 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) line 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.DLetter@mm, click Delete.

    3. Reversing the changes made to 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, and 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:

      "DeathLetter" = "%System%\DeathLetter.vbe"
    5. Navigate to the key:

      HKEY_CURRENT_USER\Software\Kazaa\LocalContent\
    6. In the right pane, delete the value:

      dir0   "012345:%system%\GEDZAC_LABS(P2P)
      DisableSharing  0
    7. Navigate to the key:

      HKEY_CURRENT_USER\Software\KAZAA\ResultsFilter\
    8. In the right pane, delete the value:

      virus_filter  0
      firewall_filter  0
    9. Navigate to the key:

      HKEY_CURRENT_USER\Software\Gedzac Labs

      and delete it by pressing the DELETE key.
    10. Exit the Registry Editor.

    Writeup By: Jason Pan