We have presented host security problems in a theoretical and a practical sense. We have shown examples and sample code of how the problems in host security can be exploited. We have shown host security problems exist both in privileged and unprivileged modes. We have also shown how easily problems on the host can be exploited. Problems such as Denial of Service and backdoors have been discussed and illustrated. Nowadays, all hosts form part of a network. We continue to discuss security problems at a network level.