WordPress is the most popular used blogging/CMS software which is why I guess it is used by millions of websites around the world. Unfortunately, there are some very bad people out there that will try their hardest to exploit any weaknesses in your blog. If you look through your logs you can guarantee that someone, or something, like bots, for example, has tried to gain access to your site by attempting to access your login page, registration page or even your forgotten password page. Of course, you can never completely eradicate the bad boys but with a good knowledge of WordPress security can help you protect your site as much as possible.