They Know What You're Shopping For

The widening ability to associate people's real-life identities with their browsing habits marks a privacy milestone, further blurring the already unclear border between our public and private lives. In pursuit of ever more precise and valuable information about potential customers, tracking companies are redefining what it means to be anonymous. The use of real identities across the Web is going mainstream at a rapid clip.

A Wall Street Journal examination of nearly 1,000 top websites found that 75% now include code from social networks, such as Facebook's "Like" or Twitter's "Tweet" buttons. Such code can match people's identities with their Web-browsing activities on an unprecedented scale and can even track a user's arrival on a page if the button is never clicked. In separate research, the Journal examined what happens when people logged in to roughly 70 popular websites that request a login and found that more than a quarter of the time, the sites passed along a user's real name, email address or other personal details, such as username, to third-party companies. One major dating site passed along a person's self-reported sexual orientation and drug-use habits to advertising companies.