You can set your event (and hence its registration) to private if you don't want to allow just any random person to register for it.
Setting Your Event to Private
There are 2 situations where an event can be set to private:
When creating an event
If you are creating an event, the Privacy setting is in the Create New Event step itself, just after the Organizer field:
When you have already created your event
if you have already created your event, the privacy setting is under the Event Page section, which is accessible from the left hand navigation:
Private Event Settings
There are 3 possible settings when you choose the Private option:
1.Attendees can share the event with their friends on Facebook, Twitter and LinkedIn.
Turning this off will hide the social sharing icons on the event page such that users are not able to share the page
2. Invitation Only - Attendees must receive a GEVME email invitation to register.Selecting this option means that participants will only be able to register for your event by clicking on a Call-To-Action (CTA) button that you would have sent them by email. This means that you will have to send the invitations for your event exclusively from GEVME if you choose that option (see the article XXX to learn more about how to send an invitation email with a CTA button to register). If a user navigates directly to the URL of your event page without clicking on the CTA button in the invitation email, they will be presented with the following message on the event page:
3. Password Protected
Choosing this option will require the participant to enter a password in order to access the event page: