After installing a X11 client like Exceed or Xwin
you will find that it is set up with no X windows security whatsoever. By
default anyone has access to your screen and keyboard that allow them to access your system running Exceed or Xwin32. Access to your screen gives people the ability to create windows on it, or to
read any part of your screen or even to intercept the mouse and more dansgerously you keystrokes (like passwords). Follow these step by step instructions to start accessing someone else display on a PC or Unix.
First log into a Unix like system and do the following command to see the content of the catured display.
% xwd -root -display A_PC:0.0 -out disp.xwd
And those command to see the content of this image (an xwud image Dump).
% xwud -in display.xwd
or
% xv display.xwd
you may have problem seeing the dump if your display have less color than the captured screen.
Then you may want to use xpr to downgrade the image quality.