Events + FB/Twitter Integration allows any FB/T user to modify events?

I've enabled Facebook and Twitter Integration for logging in and attending events. Once logged in the person is given a WordPress account and going to the backend of that WordPress account they are given access to the Events + admin panel and can add/modify events - this cannot happen!

How can I completely disable the WordPress backend for them, I only want them to be able to login in with Facebook/Twitter to click attending - they should not see the WP admin bar on the top of the site or be able to access the backend at all, even to modify their own profile - all they should be able to do is use the facebook/twitter login screen when they click on one of the attending buttons.

Thanks,
Thomas