Preventing Double Registrations

[The Equivocate]

What are all the steps I can take to ensure someone does not register more than one account? What options can I change, what hacks can I install, etc?

[Carnage]

theres an option in the admin cp that allows you to prevent multiple registrations.

[The Equivocate]

But that option is too easy to get around, it just works with cookies that can easily be deleted. I need something that at least works with IP's.

[007]

Same... been searching but with no luck! :(