The local CERT authority DK-CERT https://www.cert.dk/nyheder/nyheder.shtml?11-04-14-13-56-26 reports that thre has been a server breach at wordpress. Also the company behind wordpress blog software is encouraging their users to change password. http://en.blog.wordpress.com/2011/04/13/security/
They report that the hackers gained access to several of their servers and gained root access. They do not at the moment of this writing know what was stolen or revealed, but they are reviewing their log files.
If you use the same username and password for more than the blog site you should also change your password at those sites.
Here is a link to Sophos Security about the hacking of wordpress and a guide to change your password.