Ti be sure you don't have an ongoing gong show happening and your log-in information is secure please make the following changes where applicable.
Thanks for confirming the URL in question here.
Who has access to your login information? Change it now and do not provide it to anyone ever again.
Did you use the same password for your email account and your blog? Change it now and do not provide it to anyone ever again. Go to your email program and change the password to a very difficult one because that's how many hackers gain access to blogs.
Are you sharing log-in information with anyone or leaving it where anyone can locate it? Never ever do that.
Is your password a weak one that others can easily guess? Create a strong password. Change your blog password to a very difficult one > http://en.support.wordpress.com/passwords/#change-your-password
Are you remaining logged in on your computer so anyone can come along and access your blog through it? Always log out.
Please read http://en.support.wordpress.com/security/
1. Log-in go here > Users > All Users and delete any user that does not belong there.
2. Disable post by email > http://en.support.wordpress.com/post-by-email/
3. Disable post by voice > http://en.support.wordpress.com/post-by-voice/
4. Use a secure, encrypted connection to connect to your Dashboard. Under Users → Personal Settings, check the box that says “Always use HTTPS when visiting administration pages, and click Save Changes.