How facebook (and yahoo now) knows who I am?

[Paul]

I gave them false name and age and email when registering.
I put password which I never used anywhere.
After I logged in in Y! Answers using fb, it displayed some error and my fb account was logged out.
I logged in, and it showed security check saying something like 'you are trying to make fake account....possible reason: you are pretending to be someone who is not you...'. It asked to comfirm codes on image and give them phone number...and finally accepted me.
Worst of all it automatically selected my real city as city, even that I told that I am in another country....so, here I am at yahoo....but they now have evidence who I am....

IS IT BECAUSE THEY CHECKED IP ADDRES OR THAT NAME?
BECAUSE I USED NAME FROM SOME POPULAR PERSON?

[Nick Gillotti]

Yes, your IP is always tracked back to your general location. Websites use this information simply as a comparison between the tracked IP, and the given information to establish wether a person, or a computer is attempting to make a fake or "ghost" account. Since these ghost accounts are usually used in a way that violates a websites terms of service, they have to have a way that shuts them down before any damage can be done (I use the term damage loosely).