An extremely insecure X11 security program that makes use of a host-based authorization list. With this, anyone from localhost can sniff your X server's keyboard events, look at your screen, or even send keyboard events to your terminal's shell (though xterm isn't vulnerable to this sort of attack, gnome-terminal and others are)
Alternatives include
xauth and
ssh-agent, which are based on
cryptography. However, even with these
measures, the
xhost list is still checked, which can go
unnoticed. For the truely
paranoid, there's a quick script-like
C program I wrote at http://members.tripod.com/andy_779/xhost-rm.c that I put in my
crontab and
PPP init script to clear this list
regularly.