WordPress 2.5.1 was just released yesterday to fix one very important security vulnerability. Although the details of the vulnerability has not yet been made public, it will be soon. If your WordPress blog supports open registration (as do most default installations), it is particularly important to upgrade. There’s also a bunch of other bug fixes and performance enhancements, so it is a good all-around upgrade anyway.
Could you tell what was the vulnerability? How can I protect myself from being hacked?