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05 March 2001
13 February 2007

VBS.Kidarcade is a virus based on Visual Basic Script (VBS). It has been put into an HTML page, and is on at least one Web site. The virus installs a Backdoor Trojan that allows unauthorized access to the infected computer.

Antivirus Protection Dates

  • Initial Rapid Release version 06 March 2001
  • Latest Rapid Release version 28 September 2010 revision 054
  • Initial Daily Certified version 06 March 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.

VBS.Kidarcade is both a Visual Basic Script and a JScript virus. It utilizes the Scriptlet.TypLib ActiveX control, which allows local files to be created or modified. Microsoft has released a patch that eliminates security vulnerabilities in Scriptlet.TypLib. The patch removes the "safe for scripting" marking, thereby causing Internet Explorer to request confirmation from the user before loading the control. The patch is available at:

VBS.Kidarcade performs the following actions:
  1. If the security settings on the computer allow the scripts to run, then the HTML page may copy the viral Visual Basic Script file to the \Windows\StartUp folder. This file will be executed every time that Windows starts.
  2. When executed, the script will drop the binary file that consists of the decoder, written in Assembly language, and the encoded body of the Backdoor.Trojan. The script then runs the DOS/Windows utility Debug.exe to read the decoder instructions to memory and pass execution control to them. The decoder extracts the body of the Backdoor.Trojan from the binary file and writes it as an executable program.
  3. The Script then moves the Backdoor Trojan to the \Windows\System folder and runs it. The temporary binary file is then deleted.
  4. The Script may create the value


    in the registry key


    and changes the value of



    SHELL32.DLL, 36
  1. This prevents Windows from displaying the .hta file extension, even if "Hide file extensions for known file types" is unchecked in Windows Folder Options.
  2. The script may create the Wininit.ini file in the \Windows\System folder and writes the following lines in the file:

    NUL= <path> \<name of the viral script>
NOTE: When the installed Backdoor.Trojan runs, it sends the signal "I am ONLINE" to the remote computer. This tells the remote computer that the infected computer is ready for remote administration. It then starts to accept and perform the remote commands. The remote administration has full access to the file system of the infected computer. The trojan permits the remote administration to download or upload files from the remote computer, change the registry, and run commands and programs. The Backdoor Trojan is able to change its own settings and uninstall itself if such commands are received. Because the Backdoor Trojan could be dropped and launched by the viral script that might be stored in the \Windows\StartUp folder, it may run every time that the infected computer starts.


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, you need to:
  • End all network connections, scan with Norton AntiVirus, and delete files detected as VBS.Kidarcade or Backdoor Trojan.
  • Remove the text that refers to the viral script from the Wininit.ini file.
  • Delete NeverShowExt from HKEY_CLASSES_ROOT\htafile

The following sections offer detailed instructions.

To scan with Norton AntiVirus:
  1. Make sure you have no network connections (unplug the network card and disconnect your Dial-Up connection if any).
  2. Run LiveUpdate to make sure that you have the most recent virus definitions.
  3. Start Norton AntiVirus (NAV), and run a full system scan, making sure that NAV is set to scan all files.
  4. Delete any files detected as VBS.Kidarcade or Backdoor Trojan. If any files are detected as VBS.Kidarcade or Backdoor Trojan, then when the scan is finished, reboot the computer and repeat the full system scan with NAV.

To edit the Wininit.ini file:
  1. Click Start, point to Find, and click Files or Folders.
  2. Make sure that Look in is set to (C:) and that Include subfolders is checked.
  3. In the Named box, type wininit.ini and click Find Now.
  4. Double-click the Wininit.ini file that was found in the \Windows\System folder. It will open in Notepad.
  5. Look for the line <path>\<name of the viral script> and delete it if found. The <name of the viral script> could be different for the VBS.Kidarcade variants. As a recommendation, look for the viral script files, detected by Norton Antivirus as VBS.Kidarcade on the previous stage.
  6. Save the changes and close Notepad.

To edit the registry:

CAUTION : We strongly recommend that you back up the system registry before making any changes. Incorrect changes to the registry could result in permanent data loss or corrupted files. Please make sure you modify only the keys specified. Please see the document How to back up the Windows registry before proceeding.
  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:

  5. Close the Registry Editor.

Writeup By: Serghei Sevcenco