This is nothing to do with logic, but it is perhaps to do with silliness. Facebook recently offered users the chance to get their own, unqiue link on the site, so they can send people a URL which takes them directly to their page.
It seems that some people have bookmarked this URL, and are using it as their default page to access facebook. They see their newsfeed and so forth when they go there.
So far, nothing too surprising - until you remember referal tags. When you browse the web, your browser tells the site you're going to where you came from. So if I search google for the BBC, for example, then if I click the first link in google, then the BBC web server will be sent a tag which tells them that I came from this page:
http://www.google.co.uk/search?q=bbc
If you go to the Facebook page with your unique address and click on a link in your newsfeed, then the site you are visiting gets to know exactly who you are in real life.
If your privacy settings are not locked down, then they could also easily obtain have a whole bunch more about you too - anything you have on Facebook, in fact. You'd think Facebook would have considered this, and had the unique URL redirect to something more generic, but it seems to have been overlooked.
Which I find a tadge uncomfortable. So I'm letting people know.
