Loads of spam registrations

We are getting loads of spam registrations. They are signing up and posting rubbish to their profiles. How can we stop this? I have looked at the plugin and clicked ‘options’ but that goes to a page with lots of snippets of code…how do I go about making changes/stopping this? Please help.

The website isn’t actually in use anymore, mainly just left up with information from a previous big event (TEDx) that we did. I have considered upgrading the plugin not sure on the impact it would have. Also considered removing it altogether. This would obviously work I guess but if normal registration remains available spam is likely to be the same/increase?

Please help. http://www.tedxdubbo.com

http://wordpress.org/extend/plugins/bp-registration-options/