During his two-day marathon testimony in Washington this week, Facebook CEO Mark Zuckerberg looked particularly uncomfortable answering basic questions about how Facebook tracks people when they're not using Facebook. In case you hadn't already heard, yes, it's true: Facebook can track your online activity even if you aren't signed in to Facebook.
He squirmed under questioning from Sen. Roger Wicker: "There have been reports that Facebook can track a user's internet browsing activity even after that user has logged off of the Facebook platform. Can you confirm whether or not this is true?" Sen. Wicker asked.
"Senator, I want to make sure I get this accurate so it would probably be better to have my team follow up afterwards," Zuckerberg responded, before being pressed and giving an incomplete answer.
The good news is that the answer to Sen. Wicker's question isn't only in a report — it's on Facebook's website in its help section. Here's how Facebook can learn about what you do online even when you're not on its platform.
Facebook tracks your browsing activity around the web with the "like" button
You know those Facebook "like" buttons you see around the internet? (There's even one on this article.) They're tracking your browsing activity whether you're a Facebook user or not. "If you’re logged into Facebook and visit a website with the Like button, your browser sends us information about your visit," Facebook's website says. "If you’re logged out or don’t have a Facebook account and visit a website with the Like button or another social plugin, your browser sends us a more limited set of info."
Here's what Facebook says it tracks when you're not logged in: "We receive info about the web page you're visiting, the date and time and other browser-related info. We record this info to help us improve our products."
Facebook tracks when you visited advertiser pages via the "Facebook pixel"
The Facebook pixel is a piece of code advertisers put on their sites that tracks your activity on those sites and reports it back to Facebook. Here's how Facebook explains how it works: "When someone visits your website and takes an action (for example, buying something), the Facebook pixel is triggered and reports this action. This way, you'll know when a customer took an action after seeing your Facebook ad. You'll also be able to reach this customer again by using a custom audience."
Facebook works with businesses to figure out when you see an ad on Facebook and then visit that advertised store, via "offline conversions"
Businesses can upload their data to Facebook to see if the ads they run on Facebook lead to sales in their stores; they do this via something Facebook calls offline conversions. Here's how Facebook's website describes them to advertisers: "Facebook's offline conversion measurement solution helps you understand which offline events, such as purchases in your retail store or orders made over the phone, happened as a result of your Facebook ads." Businesses upload their in-store sales data in spreadsheet format and then Facebook matches that data with the people that saw its ads.