I recently accidentally pressed ctrl+alt+backspace key combination. It killed my X server. To prevent it from happening again and to protect your unsaved works, you have to disable this key combination. For KDE 4.x users, below are the steps:
Open the settings page:
Menu --> Applications --> Settings --> System Settings
Open the Input Devices:
Clik on Keyboard and the Advanced tab and click on the Configure keyboard options checkbox:
Find Key sequence to kill the X server from the list and untick the check box for Ctrl + Alt + Backspace
And then click the Apply button to save the settings.
That is all there is to it. Have fun!