Facebook knows when your birthday is.
It's got a pretty good idea who your best friends are, your preferred holiday destinations and your relationship status.
So far, so obvious, right? Wrong. There's also a whole host of other data being compiled about as we speak, and doubtlessly has been since you first signed up to the site.
Information that can be used to create a profile of your personality and be used by advertisers to target you.
The info is so vast that it can accurately pinpoint your 'intelligence', political leanings, life satisfaction and even sexuality by just scanning your online activity. Which is sort of... sinster.
Researchers at the University of Cambridge have launched 'Apply Magic Sauce', a free web app that will browse your Facebook profile and charter exactly what the social media giant 'thinks' of you - and the sort of information they supply to advertisers (for a price).
Having scanned through your 'Likes' and key words in your status updates, the social scanner is able to build a profile of just what sort of personal profile you've 'built' through your activity around Facebook.
Much like the below.
Constructed by Cambridge University's Psychometrics Centre, the tool is designed to highlight just how much additional information social media sites are able to collect on you in addition to the elements you add in your profile.
"Social media mishaps have become commonplace and can end up costing someone much more than just their jobs," said Kassem Younis, founder and CEO of Thoughts Around Me.
"Users are becoming much more careful with what they post, which in turn is actually harming their ability to speak honestly and openly. In a world where there is so much for all of us to process that we judge on perception, having what you really think attached to your identity can really harm your own brand because of the missing context."
So while the rest of your mates might not know about your long running obsession with My Little Pony and that alarmingly right-wing anti-EU blog, be aware that someone, somewhere, is keeping a very good record of it.