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Suppressing Ctrl-Alt-Del and Preventing Windows Security Screen under Windows Vista and 7

    Question

  • Hello,

    I have a technical question to developers regarding the
    suppression of the shortcut "Ctrl-Alt-Del" in an application.


    Background of my query:
    -----------------------
    I'm currently working on a software which allows students
    to take exams online at the computer, in a kiosk mode,
    which shall prevent cheating during the exam.

    At the beginning of an online exam, our program creates a new
    "desktop" on the client, and starts a special Portable Firefox
    in fullscreen mode.

    The Portable Firefox (as a client) connects to an exam server,
    which is running an LMS (Learning Management System) like
    ILIAS or Moodle in a quiz mode. The Portable Firefox just
    has to know the URL for remotely starting the exam on the server.

    During the exam, the Firefox browser is running in a kiosk mode
    so it does not show an URL line and menu bar anymore,
    and so the examinee can only navigate on the ILIAS or Moodle
    pages of the exam.



    The Problem:
    ------------
    Our application suppresses certain key shortcuts like Alt-F4
    after the student has entered the exam.

    But we want to suppress also the Ctrl-Alt-Del shortcut
    to prevent the examinees from starting the Task Manager
    and from accessing other (impermissible) applications.

    Currently, our system runs on Windows XP but shall be ported
    to Windows Vista and Windows 7. Under Windows XP, you could
    simply set the Windows Registry Variable "DisableTaskMgr"
    to 1 (true) in the Registry Key

    HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Policies\System

    or ...\Explorer           rather than ...\System
    or HKEY_LOCAL_MACHINE\... rather than HKEY_CURRENT_USER

    , respectively.

    Under Windows XP, the shortcut Ctrl-Alt-Del usually calls the Task Manager
    directly, so setting the DisableTaskMgr Registry Key will successfully
    prevent the Task Manager, and pressing Ctrl-Alt-Del will show no effect
    on the screen, so the examinee remains on the exam page.

    Unfortunately, under Windows Vista and 7, the scenario has changed:

    Ctrl-Alt-Del does not directly call the Task Manager,
    but the "Windows Security Screen", which has a blue background
    and the five menu entries

    Lock this computer
    Switch User
    Log off
    Change a password
    Start Task Manager

    , see

    http://windows7themes.net/pics/windows-7-start-task-manager.JPG

    You can disable these menu entries separately by setting
    the Windows Registry keys

    DisableLockWorkstation
    HideFastUserSwitching
    NoLogoff
    DisableChangePassword
    DisableTaskManager

    to 1 (true). The Windows Security Screen then still appears,
    the five menu entries being greyed out.

    However, we want to prevent the Windows Security Screen from
    ever coming up, so the pressing of Ctrl-Alt-Del does not show
    any effect on the screen (as it is the case under Windows XP).


    Is anybody here who manages to suppress the Windows Security Screen
    per se / totally? If so, how did you achieve that
    (seen from the technical viewpoint of a Windows programmer)?

    (We are working with Visual C++ 2008 Express Edition and
    Visual Studio 2008). We can set Registry entries in our C++ Code,
    as long as we know the correct names of the Registry keys...

    but I have not heard of any Registry key which prevents
    the Windows Security Screen. Is that possible at all?



    A modified "Gina.dll", as often recommended, would IMHO be no
    solution to the problem, because the operating system does not
    use the "Gina.dll" anymore since Windows Vista, right?

    In other words: even if Gina.dll were still used by the operating system,
    it would not be helpful because under the old Windows NT, the shortcut
    Ctrl-Alt-Del came up with the Windows LOGON Screen, which the Gina.dll
    is responsible for. Whereas under Windows Vista and 7, Ctrl-Alt-Del
    launches the Windows SECURITY Screen, which is different from the
    Windows LOGON screen, isn't it?

    And under Windows XP, where die "Gina.dll" still had a function,
    we do not have the problem, since Ctrl-Alt-Del calls the Task Manager
    directly and we can disable the Task Manager via Registry
    (by the way only in Administrator mode. It would be nice if
    this were possible with a User account, too. But a User account
    is not allowed to change the Registry key for DisableTaskMgr).

    Unfortunately, till now, my Google and MSDN searches produced
    no helpful answer to this question.

    Many thanks in advance for helpful comments and advice,
    Dirk

     

    Wednesday, June 09, 2010 11:22 AM

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