See No Evil - 1.1.1

Not really helpful. If your writing something you dont want people to see, simply create a larger window of something else. Place the prvate window in front of the larger one. By quickly moving your mouse one centimeter and clicking youll switch to the larger window, and cover it up instantly. Oh yea. If you are looking at porn, this is useless annyway, because it is not like the person who enters teh room unsupectedly is walk over and examine your screen without noticing the fact the your are not wearing any pants, sitting in a computer chair, probably with a rather large erection, sweating. Oh. Kunich is hilarious. Visit his website. He is so desperate it is funny.

the product, but from reading the comments, I have a suggestion that'd be ideal, but not exactly one that might be doable: instead of showing a dark screen, or whatever it shows currently, have it display a screenshot image... full screen. If one can use one's own shot, even better. But why go to all that trouble when one can install an application switcher that shows only active applications? Watch your private stuff, keep the pointer on a spot of the desktop that remains visible, click spot if someone emerges.