This talk was prepared for IV National Free Software Conference in Universidad Mayor, Real y Pontificia
de San Francisco Xavier de Chuquisaca, Sucre, Bolivia. This is more or less the second part for my Network security talk, bringing down to earth some of the concepts to more concrete solutions (although still fairly generic).
I presented it in 2005 for UNAM's Computer Security Department's Admin-unam internal seminar; I re-wrote it as a full-text article, also available here.