More and more websites implementing "like buttons" from Facebook, Google and Twitter.
However, these buttons transmitting data to the operator of their network platforms already when the page loads – so completely without users approval.
The data contains not only the URL of the current page, at least for registered users of the platform the data is including an identifier that is directly related to a person.
Facebook & Co can also create complete data profiles of its users.
This could potentially not be compatible to the guidelines of data protection and privacy of the website owner, or according to local law.
The german "heise online" platform developed a two-stage solution which allows data transmission only with the consent of the user.