Start - your other topic where you complained about getting no support was posted in the j1.5 forum. so off topic.
the topic here probably had a lot of views and people either thought, no real information or lets go of and edit the site.
several hints here - if you know that something can be done to edit on your site by the public remove the link - screenshot it or whatever.
next hint - have a look in your acl permissions.
you must have done something to make it so that the public can fiddle it.
see this section
http://docs.joomla.org/J2.5:Access_Cont ... t_Tutorial
check the permission in each category