Go to above mentioned link. If it does not help then you may :
Download your whole site to your local desktop or PC. Open whole site in some really good text editor like espresso,coda or netbeans.
Search for this text you just pasted in all the files. Note the name of the file in which it is present.
open your web server and replace those files with fresh ones.
Possible files infected with this could be:
wp_config.php [sample],index.php , wp_settings, wp_register ,wp_login ,wp_load... Not limited to this list. I had a similar bug in my installation and I removed by restoring above files from fresh WP.
Do check if you have any upload capability on your site for users or your WP version was outdated or you are using some plugin which has outdated timthumb.php.
To avoid this in future Sucuri WordPress plugin highly recommended.