Version:           unspecified (using KDE 4.7.3) 
OS:                Linux

In much the same vein as bug #201777, this is a bug that could allow somebody to see your desktop behind the lock screen.

If KDE's Blur effect is enabled, and the lock screen is set to Blank Screen, then an unauthorized user at the computer can call up the unlock dialog, and cancel it (or simply let it time out) and there's a good chance that the desktop will become visible. The desktop image does not update, which leads me to believe that the "blank screen" window is still visible, but the Blur effect blitted the desktop onto it. This would explain why animated screensavers do not have this problem, as they will then clear and redraw the window themselves.

I haven't been able to reproduce this bug with either Blur disabled, or with any screen saver other than "Blank Screen" enabled. I am reporting this as a bug with the effect (rather than with the lock screen) because I don't think Blur should be affecting the blank screen in the first place.

Reproducible: Sometimes

Steps to Reproduce:
1. Enable compositing, the Blur effect, and the Blank Screen screensaver.
2. Lock the screen.
3. Move the mouse to call up the password dialog.
4. Click the cancel button (or wait for the password dialog to time out)

Actual Results:  
There's a good chance that a screenshot of the desktop will become partially or wholly visible.

Expected Results:  
The blank screen should have remained blank. The desktop should not have appeared.

Kubuntu 11.10 with the nVidia proprietary drivers.