Authorities are concerned by new research that claims such an attack is feasible. The Federal Bureau of Prisons is aware of this research and taking it very seriously The research team tested their work in the basement of a Washington D.C.-area home for under $2,500 before discussing their research with authorities over the summer at CIA headquarters in Northern Virginia. The systems at federal prisons are vulnerable and could behave in a similar way, putting them at risk to an attack via USB stick or if a hole is found in an internet connection.
Source: https://threatpost.com/researchers-warn-prison-hacks-opening-cell-doors-110811-0/75868/