Richard Stallman Quotes
If there is a Like button in a page, Facebook knows who visited that page. And it can get IP address of the computer visiting the page even if the person is not a Facebook user.
Stallman, Richard. "A Free Digital Society." Free Software Foundation, 2011.
Richard Matthew Stallman, also known by his initials, rms, is an American free software movement activist and programmer. He campaigns for software to be distributed in a manner such that its users receive the freedoms to use, study, distribute, and modify that software. Software that ensures these freedoms is termed free software. Stallman launched the GNU Project, founded the Free Software Foundation, developed the GNU Compiler Collection and GNU Emacs, and wrote the GNU General Public License.