Sharepoint user can view site collections he is not a member of

Question

as i understand sitecollection security ,member of a given sitecollection can not view another site collection where he has no membership ,my problem is that any user from a given site collection can view other site collection easily ,how is that ? by the way ,this user is not an administrator ,he is a domain user ,with approvers policy in his sitecollection

Answer 1

Thanks Dan for your attention ,i figured it out ,our previous sharepoint admin added authenticated users group to every site collection which allowed any user who has account on sharepoint to view other sitecollection

Answer 2

How do you have the sites setup? Are they seperate site collections under one web application or seperate site collections under seperate application pools?