New site owners getting access to main site backend


I’m having a bit of an issue. It seems that when a new user registers for a site they are being given access to the main site backend. When they log in they are taken to the main site backend and not to their site. When I look at users in the network admin area I can see that they are listed as mainsite users as well as their own sites. I’m sure this must be somekind of settings issue, Any suggestions as to how to insure that users only have access to their own sites admin area and not the main site admin area.

Thank you