I read that many people have a problem with "spam user registrations". I try to work on a solution but i have a little problem to implement it : ( Maybe some one can help me!
In my case: users who create an account are some of my clients, so my idea is:
I send an email to my client with the link to register and a keyword to insert in a extra field on the registration page.
The idea is to check that the extra field is similar to the one given (always the same). I check on the admin: User management -> Access rules page but i can't add a rule on an "custom" field