Facebook
has long kept track of the websites its users visit when they aren't on the
social network. Three months ago, it began using the data to build more
detailed user profiles, allowing advertisers to target people with more personalized marketing
pitches.
That
has rankled some retailers, advertisers and Internet publishers, which worry
that the wider use of browsing history will hand Facebook, and potentially
their own rivals, more information about existing and prospective customers.
Companies
that want users to share content on Facebook install a small bit of Facebook
code, called a
pixel tag, on
their sites; the pixel is often associated with Facebook's "Like" and
"Share" buttons. Many websites have installed the code, allowing the
social network to record a significant amount of Internet activity.
Facebook
places another bit of code, known as a cookie, on its users' computers. When a user visits other websites
that have Facebook's code, Facebook can recognize the cookie, building a record
of how the user surfs the Web.
Facebook
also can track users on their phones. Some mobile app publishers, aiming to
optimize their advertising on the social network, let Facebook know the unique
hardware identifiers of their app users. Facebook can match the IDs to those of
its own mobile users.
(In
order to access Facebook, all users are required to agree to the company's terms of service, which allow for such data to be
collected.)
To
be sure, many other companies, including Google Inc., GOOGL +1.08% track the browsing histories of Internet
users to help target advertising.
But
advertisers say sending information to Google doesn't scare them as much as
sending information to Facebook, mainly because Facebook knows users' real identities.
Courtesy -Wall Street Journal Sep 23rd 2014
