"Did you know that more than 73 million web sites in the world run on the WordPress publishing platform? This makes WordPress more popular than Microsoft SharePoint, Blogger, or Drupal. It also means that WordPress is a large target for hackers.
Half of the WordPress sites out there are self-hosted, which means that the WordPress administrator carries the lion's share of responsibility for a secure installation. Out of the box, there are several ways that WordPress security can be tightened down, but only a fraction of sites actually do so. This makes WordPress an even more popular target for hackers.