If you are naked and don't want to be seen but want to know who it is that you hear coming, you might step behind a hedge and just peak through. But do you know if the owner of the hedge is back there behind you with a full view of your backside?
...that is a metaphor for people who make obscure names for themselves and then repeatedly use those names in web IDs by which they chat, visit forums, blog and so forth...they almost make it easy for the marketer or phisher who is sifting the net for real names to manage an uncloaking. So say researchers at INRIA.
You can test that special bit of privacy armor you forged for yourself right here.
I did. My moniker greensmile is would not be identifying until the population of the planet shrank to 1.4 billion. But the gmail ID behind it is a friggen lighthouse with my name on it.