Hidding your page with the CSS trick display:none is pure illusion.
It’s not by changing the wallpaper that you lock your door !
The screen is effectively blank, but the datas are all visible by using right-click “view page source”.
Demo link to “a blank screen”: http://www.netajour.com/buddytest/test.html
If your datas need privacy, you have to use something better as display:none;