If your site has been hacked, you'll need to go through ALL of these resources and get it completely cleaned up:
http://codex.wordpress.org/FAQ_My_site_was_hacked
http://wordpress.org/support/topic/268083#post-1065779
http://smackdown.blogsblogsblogs.com/2008/06/24/how-to-completely-clean-your-hacked-wordpress-installation/
http://ottopress.com/2009/hacked-wordpress-backdoors/
Additional Resources:
http://sitecheck.sucuri.net/scanner/
http://www.unmaskparasites.com/
http://blog.sucuri.net/2012/03/wordpress-understanding-its-true-vulnerability.html
See also:
http://codex.wordpress.org/Hardening_WordPress
BTW, if you have a backup of your site from before the hack happened, restoring from that backup may be the easiest way to go.