Separating administrator content from user content

Hello,

My name is Manu Cuche. I am currently in my third (and last) year of computer science at Lessius Mechelen College. I have recently started working on my final project. For this project I have chosen the subject of security in Drupal, more specifically about separating administrator content from user content. I understand that this is a known issue in Drupal, and my first goal is to properly understand and define this issue. To do this I would like to ask for your help.
I am looking for people who were already confronted with problems concerning above mentioned isue. If you are one of those people, or know someone who has been confronted with a problem, I would very much appreciate it if you would contact me.

Thanks in advance.