Can you lock GTW registration email to a company domain (users must have a valid comp email) to access meetings or at least be forced to provide a valid one or prompted to await Organizer approval before been allowed in the meeting if they're using a different address/domain?
We've seen a series of security breaches where an attendee link is shared and random users can sign in with fake emails to attend our meetings.
I'm afraid GoToWebinar join links can be reused several times in order to allow for an attendee to switch devices if necessary while in session. My advice in this scenario is to keep an eye out for duplicate attendee listings through your GoToWebinar control panel, while broadcasting live.
GoToWebinar Organizers may also set their registrations to 'approval only', so that only pre-screened registrants will receive a join-link to the broadcast.