Here is an amuzing story where prisoners in a maximum security prison managed to hack their lockdown computers.
Their computer seems to be more like a dumb terminal than a full featured one, and what they can do and where they can go is very limited (i.e.: watch television and receive call).
However, the prisoners found out that by opening 200+ windows explorer they could cause a buffer overflow which then allowed them more access!

http://gcn.com/articles/2011/05/30/colorado-prison-sidebar.aspx

and to go with this story here is a photo I came accross on the internet and that summerize the security state of many companies!