For the past couple of months Wordpress has been working for introducing new features for the version 2.9 and also they have been working on trying to make Wordpress as a secure as possible. Moreover, during this process Wordpress identified a number of security hardening changes and improvements to make the site as secure as possible.
The headline changes in this release are:
•    A fix for the Trackback Denial-of-Service attack that is currently being seen.
•    Removal of areas within the code where php code in variables was evaluated.
•    Switched the file upload functionality to be whitelisted for all users including Admins.
•    Retiring of the two importers of Tag data from old plugins.

At the same time, Wordpress recommends all sites to be upgraded to this new version in order to ensure that you have the best available protection. If you feel that your site is being hit by the recent exploits and you want to make sure that you have cleared out all traces of the exploit, then you are recommended to take a look at the Wordpress Exploit Scanner from the link given below.

Update