Wordpress operates on PHP.  If someone wants to hack or website, it is the hosting companies job to limit them but its your job to make sure all of your passwords are considered strong passwords

First thing i would recommend is to make sure all passwords to any admin area are changed.

Read the article Gyi suggested http://codex.wordpress.org/Hardening_WordPress

For these reasons I have recently launched my own web hosting company because I want to offer the most secure environment for my customers.

If you need any help or have any questions with your wordpress securing, PM me and I would be happy to assist you.