When you create an Adobe Connect meeting room you may:
. set the meeting as an open meeting so that anyone with the URL can enter the meeting room
. set the meeting as a closed meeting for those in the participants list only.
You may also restrict the access by choosing "Only registered users and accepted guests may enter the room". In this way, if anyone tries to enter the meeting room as guest while you are logged in, you will receive a request to accept or decline the guest's entrance.
The meeting host can also block the access by ending the meeting or put it on hold.