I'm working in a hostel that has a computer for the guests to use. this computer (a simple nettop) was struggling with all the stuff it had, plus Vista, so I installed ubuntu 11.10. It's nice, clean, legal and fast. So far, so good.
What worries me is that it's a pretty standard ubuntu installation, because I really don't know how to set up an internet kiosk. You can, for instance, open a terminal.
So, my question is: what is the worst a possible linux-knowing troll could do, using the terminal, without having access to the root password?