You probably believe that your Twitter message can be seen only by your followers, this is not true. Most Twitter users do not know that their posts are visible not just to heir followers but to the entire world. The default setting on Twitter is to allow the entire world to view posts. If you want to restrict access to only your circle of people then you must change your profile setting. You have to set it to Make my Tweets only visible to my followers. This limits the access and also makes it invisible to search engines. I think it is important to do this.