You can disable CTRL+F4 button with Advanced Internet Kiosk.
Advanced Internet Kiosk by Softstack can disable system and function keys and key combinations. Download the program, install it and run kiosk.exe. Click the "Disabled keys" button of the toolbar to your left. You'll see the list of the keys you can disable. Put a checkmark in a box near 'Disable... button'. You can disable all the system and function keys and key combinations on your PC. This option is, however, disabled in the Locked mode, as it needs the system to be fully rebooted to disable or enable keys. After you selected the keys to disable click Save button in the upper-left corner of the main window. The button will grey out if the changes are saved properly. download the Advanced Internet Kiosk