Security is not new. Already the Romans tried to defend themselves against intrusions by enemies. Techniques both in defence and in attack became more sophisticated over the years. Being secure is part of military thinking. Defense in depth is a military term. The military use of ICT has grown over the past decades as it has in the civilian world. This makes it a new target and it makes military vulnerable which requires new thoughts on defence. Within a military operation, but also prior to a mission during exercises and preparation.