Came here to reminisce about xroach.

Back in the day, it wasn't uncommon that the security configuration of an X workstation was open to external windows/display. e.g. you could run a program on your system, but target your neighbor's display.

I think universities did this to make it easier to help/troubleshoot a workstation remotely, but once you figured out the commands, xroach was one of my favorites to run on another machine.

It was just the default setup for X in general. You had to lock it down to avoid it. My goodness that was sooo much fun though. ;-)