Threat Explorer

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26 September 2002
13 February 2007
Also Known As:
VBS/Corica-A [Sophos], VBS/Corica@MM [McAfee], VBS_CORICA.A [Trend], VBS.Corica [CA]
Systems Affected:

VBS.Corica@mm is an email worm that sends itself to all contacts in the Microsoft Outlook Address Book. This worm also makes several modifications to the system registry and to Active Desktop to display its messages on the Active Desktop and when attempting to edit VBS scripts.

The email will arrive with an attachment named Microsoft.vbs. The subject of the message will be either "Hi" or "Hola."

Antivirus Protection Dates

  • Initial Rapid Release version 27 September 2002
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 27 September 2002
  • Latest Daily Certified version 28 September 2010 revision 036
  • Initial Weekly Certified release date 02 October 2002
Click here for a more detailed description of Rapid Release and Daily Certified virus definitions.

When VBS.Corica@mm runs it performs the following actions:

The worm first changes the Internet Explorer default home page to a Latin-America Web portal Web site. It then copies itself to C:\%windir%\Microsoft.vbs and sets the hidden attribute for the file. The file uses a default Microsoft icon.

The worm then adds a value that points to this file in the HKEY_CURRENT_USER\AutoSetup\Startup registry key. (If the key does not already exist, the worm creates it).

The worm then creates C:\%windir%\Microsoft.txt and writes two lines of Morse code in the file.

NOTE: %windir% is a variable. The worm locates the Windows installation folder (by default this is C:\Windows or C:\Winnt) and uses it as a destination folder.

The worm then modifies the (Default) value of the registry key



Notepad.exe c:\%windir%\Microsoft.txt

The Morse code message will now appear whenever you right-click a .vbs file and click Edit.

Next the worm appends a line to the system's C:\%windir%\Applications Data\Microsoft\Internet Explorer\Desktop.htt file. This line modify the default Web page used for the system's Active Desktop. If Active Desktop is enabled, the following message appears on the Windows desktop, with "Viva Costa Rica!" scrolling across the bottom:

The worm then modifies the following registry keys to make this HTML document the system's default wallpaper:

HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Desktop\General\Wallpaper
HKEY_USERS\.DEFAULT\Software\Microsoft\Internet Explorer\Desktop\General\Wallpaper

It then checks the system for the existence of Microsoft Outlook. If Outlook exists on the system, the worm sends email to all contacts in the Outlook Address Book, as follows:
  • If the default contacts folder for Outlook is named "Contactos," the email message is sent in Spanish:

    Subject: Hola.
    Message: Aqui te mando un anexo muy importante que lo abras.
    Attachment: Microsoft.vbs
  • If the default contacts folder for Outlook is not named "Contactos," the email message is sent in English:

    Subject: Hi
    Please open the attachment is very important.
    Attachment: Microsoft.vbs

The worm then adds the following registry key to the systems registry:


and sets the value to "Costa Rica."


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.

NOTE: These instructions are for 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 files that are detected as VBS.Corica@mm.
  3. Reverse the changes that the worm made to the registry.

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

To update the virus definitions:
All virus definitions receive full quality assurance testing by Symantec Security Response before being posted to our servers. There are two ways to obtain the most recent virus definitions:
  • Run LiveUpdate, which is the easiest way to obtain virus definitions. These virus definitions 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 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.

To scan for and delete the infected files:
  1. Start your Symantec antivirus program, and make sure that it is configured to scan all files.
  2. Run a full system scan.
  3. If any files are detected as infected with VBS.Corica@mm, click Delete.
  4. If you use the Active Desktop, restore C:\%windir%\Applications Data\Microsoft\Internet Explorer\desktop.htt from a clean backup.
  5. Using Windows Explorer, delete C:\%windir%\Microsoft.txt.
NOTE: %windir% is a variable. The worm locates the Windows installation folder (by default this is C:\Windows or C:\Winnt) and uses it as a destination folder.

To delete 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 key

  4. In the right pane, double-click (Default).
  5. Delete the current value data, and replace it with the correct value.

    NOTE: This value varies with the operating system, and on some systems, the installation path. To determine this, you may need to look at that same key on a properly functioning computer that has the same operating system and configuration. Two common values are:
    • Windows 98: C:\Windows\Notepad.exe %
    • Windows 2000: %SystemRoot%\system32\NOTEPAD.EXE %1
  6. Navigate to the key

  7. If you know that you had a program that was using this key, and you know what goes there, replace the value that the worm added with the correct information. If you do not know, or are not sure, just delete the key.
  8. If you use wallpaper, browse to these keys:

    HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\
    HKEY_USERS\.DEFAULT\Software\Microsoft\Internet Explorer\
  9. Change the value of both to

  10. Exit the Registry Editor.

Writeup By: Brett Johnson