The vast amount of personal information people post on social media sites, combined with the fact that social media companies can now link online behavior to physical locations is creating the biggest shift in marketing since the onset of the Internet. Micro-targeted ads were only the first step; now companies can easily link anyone’s social media profile to their web-browsing habits, and sell that information to anyone who’s interested. Google, Apple, Facebook, Microsoft, and others are, predictably, jockeying for lead position.