i have a similar story, but the results didnt have any damage
i remember when i was in college going to class, and coming back.. fire up netscape, maximized and went to the course page for an economy class or something
1: i NEVER maximize my browser window, i hate maximized windows
2: i wasn't taking any economy classes (and i had netscape to start up with the last page visited since there were several sites that i visited repeatedly and couldn't choose which to make the home page

)
well.. that computer has a keyboard lockout (like an actual LOCK on the case) that locks the kb, and the mouse
after that day i locked my computer whenever i left for more than ~30 mins
i dont mind people using my stuff
but christ ASK
dont help yourself (unless i say up front you can use it

)