blog settings?

Is there a way to set a default on my Livejournal blog that will automatically allow Friends to post but everyone else (Livejournal user or not) to automatically Screen?  I'm seeing a recent increase in spammers using my blog to post ads.  I delete them promptly, but I really dislike the idea of closing my journal to public comment.



Would this map have anything to do with the change?  I usually don't check my own profile page, but I did it this morning after deleting some more spam.  I had viewers from more continents than I knew about previously.  Did I somehow become popular, or is it just that spammers have infected machines in all these locations?