Facebook is a much more open and less private social network than people think; an example is that if when a London user signs up, he is automatically placed on the Greater London network, which allows anyone within this network to see each other's profiles. However, there are a mass of different privacy settings within Facebook, and most users don't fully use these - an example of this is the public search option; even if you are not signed up to Facebook at all, unless you deselect the public search option, your Facebook profile can be found on Google, or any other search engine.