This is really interesting: Dark Stalking on Facebook
“But by far the most interesting part of all of this have been dark users. Like dark matter, these users are not directly observable, usually because they’ve completely disabled API access. In fact, some of these users are completely dark unless you’re a friend. They don’t show up in search results. They don’t show up on friends’ lists. You can’t send them messages. If you try to navigate to their user page (assuming you know it exists), you get redirected back to your homepage. These users have their privacy settings turned up real high, and are supposed to be hard to find.
However like dark matter, dark users are observable due to their effects on the rest of the universe. If a dark user comments on a stream entry, I can see that comment. More importantly, I can see their user-ID, and I can generate a URL to a page that will contain their name. I can then watch for their activities elsewhere. Granted, I can’t directly search for their activity, but I can observe their effects on my friends.”
So, even if you think you’re cloaked safely in the thermocline like a lurking nuclear sub (by using “safe” Facebook practices), the very act of trying to be invisible can give you away. You cannot be detected directly, but you invariably leave clues just by being there. I keep wondering what form the Great Facebook Meltdown will take, but it’s definitely building up to that definitive moment.