WordPress 2.8.5 has just been released:
As you know over the past couple of months we have been working on the new features for WordPress 2.9. We have also been working on trying to make WordPress as secure as possible and during this process we have identified a number of security hardening changes that we thought were worth back-porting to the 2.8 branch so as to get these improvements out there and make all your sites as secure as possible.
It includes a fix for a trackback DoS attack that’s apparently going on at the moment. I’ve updated the 3 blogs I look after with a quick
svn switch http://svn.automattic.com/wordpress/tags/2.8.5.