If you "like" a page on Facebook, you might also be opening the door to give advertisers access to your Facebook friends. Advertisers can now pay to feature stories you like so that your friends will see them, but users still have some level of control over what gets shared.
How It Works
Facebook's Featured Stories help page explains how the new ads work. In the help page example, a user likes a gym and, depending on how the user shares content, that story then shows up in the news feeds for that user's friends, which then allows ads — or "featured stories" — to appear in their friends' timelines.
Sponsored stories already appear in the right-hand column of Facebook pages, but the name will be phased out and replaced with "Featured Stories." For now, most users will only see about one featured story per day, unless they visit their news feed "a lot," according to the help page. How many visits qualifies as "a lot" is still unclear.
Don't Like It? Just Unfriend
Users can stop seeing featured stories by hiding individual stories, limiting the volume of stories they see from a specific friend (the friend who "likes" pages, which then serve you featured stories), or stop seeing certain kinds of stories by unliking the page or unfriending the person. Yes, the help page actually recommends unfriending someone as a way to stop the ads from appearing in your timeline.
Stop the Adness
Hate the idea of giving advertisers access to your friends? In theory, you can control this by adjusting your privacy settings.
If you only share the pages you like with yourself, then your friends won't see those likes — or the accompanying featured stories — appear in their timelines.
Of course, you might still see featured stories for the pages you've liked in your news feed, and your friends with looser privacy controls open the door for advertisers whenever they like something, check in somewhere, play a game or use an app.
Loose Privacy Practices
Facebook has a long, checkered history of privacy concerns, which led to an open letter from Sophos in April 2011. In that letter, Sophos requested three things from Facebook: Privacy by default, vetted app developers and https for everything. In response, Facebook rolled out two-step authentication and expanded secure browsing.
The featured stories are just starting to roll out, so it's too early to see how users will respond. No doubt many users will take another close look at their privacy settings, and maybe even reevaluate the friends they keep.