&quot;An ordinary unprivileged user with sufficient knowledge of the system needs only the ability to be able to modify machine-code in order to penetrate the system completely.&quot;<p><a href="http:&#x2F;&#x2F;citeseerx.ist.psu.edu&#x2F;viewdoc&#x2F;download?doi=10.1.1.162.364&amp;rep=rep1&amp;type=pdf" rel="nofollow">http:&#x2F;&#x2F;citeseerx.ist.psu.edu&#x2F;viewdoc&#x2F;download?doi=10.1.1.162...</a><p>Security was hard then and continues to be hard now. It would also be nice to have a cost comparison between the various alternatives.