Detect Different Machine using Browser

Question

Some webapps like Facebook and gmail, detects the first time we try to login for the first time in one machine.

Assuming that a browser can't read machine name, and MAC ADDRESS. What kind of variables are they collection for doing this validation?

Answer 1

They check for cookies, which are stored by the browser on the client pc and sent to the servers. If there is no certain cookie present they assume it is the first time.

Image source: https://en.wikipedia.org/wiki/HTTP_cookie