It's probably because it's been cast out into general public in several venues... I've killed quite a few spammers in there lately, and had occasion to spot some odd usernames...
Hint. If you see a odd 'new' username (hard to judge since many usernames are seemingly odd) click on it and look at their profile... Zero posts and no profile data (or a foriegn location) often means a Spammer signed up... Send a PM to an admin ASAP and we can usually nail them before they strike.
Hint. If you see a odd 'new' username (hard to judge since many usernames are seemingly odd) click on it and look at their profile... Zero posts and no profile data (or a foriegn location) often means a Spammer signed up... Send a PM to an admin ASAP and we can usually nail them before they strike.