Casino Spammers Hit WP Blogs?

I surf a blog traffic builder called Blog Explosion and both i Blogosphere Zoo and my g/f new WP blog Passions Within have been hit along with this permalink at I Hate Spam ~Forgetful Of Tombs.
Ok so i added some words to the spam option, seemed to work – My question though is, my g/f blog was barely up not even listed last night 10:00pm est, NO LINKS yet, and when we awoke this morning at 5:00am est, appx 7 hours later, they had hit her. How did they know she had this blog? is there a WordPress ‘Weblog’ hub like WebLog.Com?
While i am asking how can we pervent spammers? and as my blog Blogosphere Zoo is an everyone can post blog and ban naughty people that may sign up to post spam?
thank ya much? (with a southern accent)