Threat Explorer

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30 August 2001
13 February 2007

VBS.Cuerpo.A@mm is a mass-mailing Visual Basic Script (VBS) virus/worm. It is polymorphic in structure and sends itself using Microsoft Outlook. It is embedded in an HTML email message. If the HTML file is opened, and allowed to run, it drops a .bat file that causes the worm to spread.

NOTE: Some email systems will convert an HTML message to an attachment. Opening the attachment will have the same result.

Antivirus Protection Dates

  • Initial Rapid Release version 30 August 2001
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 30 August 2001
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date pending
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

If the HTML message (or attachment) that contains the worm is opened and allowed to run, it performs the following actions:

NOTE: If your system is set to use system defaults, you will be prompted before the script runs.
  1. It drops the file C:\Windows\Winstart.bat and runs it.
  2. Winstart.bat attempts to create a registry import file with a random file name such as "C:\Suioacr.reg."
  3. Winstart.bat appends text to the C:\Autoexec.bat file to run the registry import file.
  4. Winstart.bat then copies itself to the Windows folder with a random name such as C:\Windows\Fkltbie.vbs.
  5. It also attempts to copy itself to the following folders:
    • C:\Windows\Startm~1\Programs\Startup
    • C:\Windows\Menud?1\Programmes\Dnarrage
    • C:\Windows\Men?In~1\Programas\Inicio
    • C:\Windows\Alluse~1\Menuin~1\Programas\Iniciar
    • C:\Windows\Startmen?Programme\Autostart
    • C:\Recycled
  6. The VBS script then deletes C:\Windows\Winstart.bat.

The VBS script file that is dropped by Winstart.bat does the following:
  1. It copies itself as a .vbs file in C:\Windows\System as a random file name.
  2. It drops another .vbs file in C:\Windows\System that modifies the registry as follows:
    • It adds a random name and value to the registry key

    • If the date is after the 5th of the month, it changes the home page of Internet Explorer to
    • It adds a random name and value to the registry key


      (The randomly named file that it points to will have the .vbs extension)
  3. It creates the file C:\Windows\System\Blank.html. It contains a link to
  4. It modifies the registry key

    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main

    so that the home page of Internet Explorer is set to

  5. It searches the following of Microsoft Outlook folders :
    • Journal
    • Contacts
    • Deleted Items
    • Sent Items

      If a message is found which also contains an attachment, the subject line and attachment file name are used to create outbound email messages that actually contain the virus.
  6. The worm sends email to all contacts in the Outlook address book in HTML format. The virus is embedded in the HTML message.

    NOTE: Some email systems will convert an HTML message to an attachment. Opening the attachment will have the same result.

    Each contact is sent one message. The email attachment name could be anything, but it will have "(9 Kbytes).vbs" appended to the file name. For example:

    mypic.jpg.(9 Kbytes).vbs
  7. It searches for email address in .txt, .na2, .wab, .mbx, .icq, .uin, and .dat files on all hard drives and network drives. The email addresses are stored in a string and used to create a "form submit" HTML file which has a random name. The HTML file attempts to submit these addresses to a .php file on a user home page at the domain
  8. The worm overwrites any .htm files found in C:\Windows\Application Data\Microsoft\Signatures with copy of itself.


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 worm, delete files detected as VBS.Cuerpo.A@mm, remove the line that it added to the Autoexec.bat file, and remove the value that it added to the registry \run key.

To remove the worm:
  1. Run LiveUpdate to make sure that you have the most recent virus definitions.
  2. Start Norton AntiVirus (NAV), and run a full system scan. Be sure that NAV is configured to scan all files.
  3. Delete all files that are detected as VBS.Cuerpo.A@mm.

To edit the registry:

CAUTION : We strongly recommend that you back up the system registry before you make any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure that you modify only the keys that are specified. Please see the document How to back up the Windows registry before you proceed.
  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, look for a value that points to a randomly named file. Select this value and delete it.

To edit the Autoexec.bat file:
  1. Click Start, and click Run.
  2. Type the following, and then click OK.

    edit c:\autoexec.bat

    The MS-DOS Editor opens.
  3. Look for a line that refers to


    and delete the line.
  4. Click File, click exit, and save the changes when you are prompted.

You can reset your Internet Explorer home page from within the program.

Writeup By: Patrick Nolan