How does the Facebook Like button work?

Question

I want to provide a simple piece of Javascript (or an iframe, I guess) that allows 3rd parties to embed functionality from my site in theirs. The user of said widget will be

Answer 1

I believe the Like button is using cookies to obtain your FB user information, that with additional attributes are then sent to a service endpoint.

As for security measures, an obvious would be to allow requests only from websites with given access keys.