I find this one the most worrying: "In 2008, the Massachusetts Bay Transportation Authority (MBTA) obtained a temporary restraining order to prevent a talk at DEFCON by three MIT students who had uncovered physical and logical security holes in MBTA infrastructure." I mean, the IOS guy worked for IOS, so he was divulging information that Cisco paid him to obtain. HBGary paid Aaron Barr to research anonymous, so they…
The flaws they found allowed them to obtain, according to their talk's description, "free subway rides for life", which would deprive MBTA of an unknown amount of revenue which was rightfully theirs. They wouldn't disclose the vulnerability when MBTA approached them, although they changed the description of the talk to no longer imply they would explain how to get free rides.
You can read the MBTA complaint yourself: http://www.universalhub.com/images/2008/mbtamit.pdf