如何知道用户是否拥有Facebook帐户？

Question

I need to know if the users of my website has logged to facebook in the past 30 days.

Can I know this through facebook cookies or in another way ?

Answer 1

Create a <form> that asks

1. "Do you have a facebook account?"
2. "If yes, have you logged into it in the last 30 days?"

Edit: This is an interesting post on Abusing HTTP Status Codes to Expose Private Information