Preventing spam registration /url redirect
If you don't need user self-registration then just disable that functionality.  

To do this go to :
/admin/config/people/accounts (Admin > Configuration > People > Account Settings)

And for the Who can register accounts? setting choose Administrators only.

If later on you decide that you need that functionality, you can enable it back and then just add a captcha to your user registration form, or integrate something like honeypot or logintoboggan.