Internet users tap Facebook Inc.'s "Like" and Twitter Inc.'s "Tweet" buttons to share content with friends. But these tools also let their makers collect data about the websites people are visiting.
Facebook and other sites say they don't use the tools to track users.
These so-called social widgets, which appear atop stories on news sites or alongside products on retail sites, notify Facebook and Twitter that a person visited those sites even when users don't click on the buttons, according to a study done for The Wall Street Journal.
Retailers are trying to get customers to spend more than just time on Facebook - they want them to spend money, too. But with more and more data being gathered about users and their browsing patterns on sites like Facebook and Twitter, will consumers be leery of shopping on Facebook? Dana Mattioli joins to discuss.
These widgets are prolific. They have been added to millions of web pages in the past year. Facebook's buttons appear on a third of the world's 1,000 most-visited websites, according to the study. Buttons from Twitter and Google Inc. appear on 20% and 25% of those sites, respectively.
The widgets, which were created to make it easy to share content with friends and to help websites attract visitors, are a potentially powerful way to track Internet users. They could link users' browsing habits to their social-networking profile, which often contains their name.
'Like' Button Follows Web Users - WSJ.com

It looks like spy agencies lol