How was my WP site hacked

My site, http://www.cancer-study.com, has been hacked, and I can’t login to wp-admin.

Can you say how it has been hacked and what can I do to undo the damage?
I have access to the host.

Solutions Collecting From Web of "How was my WP site hacked"

If you do a Google search, you will find many topics on this.

Here are some links:

First read this: http://codex.wordpress.org/FAQ_My_site_was_hacked

Then take a look at these links:
http://ottopress.com/2009/hacked-wordpress-backdoors/
http://wordpress.org/support/topic/268083#post-1065779
http://smackdown.blogsblogsblogs.com/2008/06/24/how-to-completely-clean-your-hacked-wordpress-installation/

If you have access to your database, login using PHPMyAdmin and change admin username / password, delete users you don’t know and change password for rest.

Then start the process of backing up data and do a clean install.

Note. If you can’t find out how they got access to your site, doing a clean install and putting back data, will still leave whatever hole open.

Also not that backdoors (links / code) could have been added to your posts, so all content must be checked before you import exported data.