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

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 ,开发者_运维问答he is a domain user ,with approvers policy in his sitecollection

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