It's no surprise that social networks and other popular sites are sharing this kind of content with advertisers.
A report in the Wall Street Journal indicates that Facebook, along with MySpace, Digg and a handful of other social-networking sites, have been sharing users' personal data with advertisers without users' knowledge or consent.
The data shared includes names, user IDs, and other information sufficient to enable ad companies such as the Google-owned DoubleClick to identify distinct user profiles. Some of the sites in question, including MySpace and Facebook, stopped sharing the data after the Journal asked them about it.
The surreptitious data sharing was first noticed by researchers from Worcester Polytechnic Institute and AT&T Labs in August 2009, who brought it up with the sites in question. It wasn't until WSJ contacted them that changes were made.
Not surprisingly, Facebook appears to have gone farther than the other sites when it comes to sharing data. When Facebook's users clicked on ads appearing on a profile page, the site would at times provide data such as the username behind the click, as well as the user whose profile page from which the click came.