Make sure that you change the passwords and upgrade to the latest version of wordpress.
One of my sites was defaced lately after I reinstalled wordpress. I decided to uninstall wordpress again, but the site still shows the defaced index page. Any ideas on what's the reason behind it?
I had to remove everything in order to remove the defaced index page.
This reminds of the thing I did when I was younger xD
But maybe the index file is still there,I once had this on a clients site,there wasnt a htm or php or any other index in the public_html/www folder,and I replaced the index.html but the site was still defaced,the host solved it somehow,so contacting them might be a option.
Here are two sites that may give you some information to better help you
How To Completely Clean Your Hacked WordPress Installation | Smackdown!
30 Things to do After Installing WordPress | Make Money Online
bogart (17 May, 2010)
I've had a lot of problems with wp blogs running version earlier than 2.7. Even on 2.7 a hacker got it and was able to make a post. But didn't deface the blog.
Many WP plugins are insecure. Check that they use the "nonce" (Number Used Once) scheme when the options are updated.
It may not be WP that is causing the problem, but one of the insecure plugins that you may have installed.
Search on WordPress Nonce for more info.
Basically, it is an easy way for plugin developers to validate that the options update was from the correct, trusted source.
Normally this code appears after the Form tag in the options part of the plugin. Where it inserts a hidden form field. And where the options are updated in the PHP code, there should be some kind of check for the Nonce, referrer page and/or the user has admin rights before any changes are made.
Otaku CMS - Import a WordPress blog and manage your site using single-page App technology
It would be a shame if WP became the next Joomla,because this reminds me of the early days of Joomla.Most people think that Joomla is insecure,it really isn't,but since everybody is developing for it,it just has to happen,not even intentionally,not everyone is the best programmer in the world.The plugins tend to be the real culprits,they open back doors into the CMS and make it possible for hackers/script kiddies to exploit them and attack your site.