For more detailed information, please see the following resources:
Geni is designed as a tool for our users to document their family history through collaborative genealogy among family members. As a result, they are encouraged to create profiles for their family members who are not Geni users.
Each user controls the privacy of their profile and the profiles that they have added to their tree. If you are concerned about the privacy of your profile, the best way to control your profile privacy is to claim your account. You can do this by joining Geni using the email address associated with your profile from this page - http://www.geni.com/family-tree/start
Alternately, you can contact the person who added you and ask them to kindly remove your information from the website as you are not comfortable having it there. Keep in mind, because there is no way to prevent this family member (or anyone else) from re-entering your information, the best solution is to claim your profile on the tree.