Last year we introduced a concept called the Database of Affinity — a catalogue of people's tastes and preferences collected by observing their social behaviors — and proposed that the greatest marketing value of social media won't come from marketing to people on social sites, but rather using this database of affinity to improve the marketing that happens everywhere else. And in 2013, several social networks started to pursue this opportunity: For instance, Facebook launched an artificial intelligence research team and Google started selling "affinity segments" targeting on its properties.

But are social sites going too far in their effort to build the database of affinity? Perhaps. Recently we've seen reports that some social networks are tracking not just the information that you choose to share, but even information you choose not to share. For instance, Facebook has admitted to studying "aborted posts" — the things people type into Facebook (as status updates, in comments, and on other people's timelines) but then choose not to post. Likewise, both Google and Foursquare apparently use their mobile apps track users' locations at all times, even when people aren't actively using those company's apps.

Users are starting to notice and take action. In late December, two men filed suit against Facebook, claiming that the site's practice of scanning private messages for data violated their privacy. While I'm not a lawyer, I hope this particular suit fails — both because this is a well established practice and because scanning what people share privately could provide invaluable insight when building the database of affinity. But if the social sites keep overstepping on privacy — especially tracking information people choose not to share with others — then this could become a big problem.

My colleague Fatemeh Khatibloo's recent report on contextual privacy argues that the collection and use of personal data must be consensual, within a mutually agreed-upon context, for a mutually agreed-upon purpose — and that engaging in poor privacy practices can literally kill a company. If the social networks want to realize the full potential of the database of affinity, without jeopardizing their businesses, they'd do well to heed Fatemeh's warnings.