J. Back, D. Furniss, M. Hildebrandt, und A. Blandford. Computer Safety, Reliability, and Security, Volume 5219, Springer Verlag, Berlin / Heidelberg, Germany, The original publication is available at www.springerlink.com. Paper presented at SAFECOMP 2008: the 27th International Conference on Computer Safety, Reliability and Security, 22-25 September 2008, Newcastle upon Tyne, UK. http://www.safecomp2008.org/.(September 2008)