If you downloaded WordPress 2.1.1 within the past 3-4 days, your files may include a security exploit that was added by a cracker, and you should upgrade all of your files to 2.1.2 immediately.
Wordpress 2.1.1 Dangerous, upgrade to 2.1.2
It was determined that a cracker had gained user-level access to one of the servers that powers wordpress.org, and had used that access to modify the download file. We have locked down that server for further forensics, but at this time it appears that the 2.1.1 download was the only thing touched by the attack. They modified two files in WP to include code that would allow for remote PHP execution.
What You Can Do to Help
If your blog is running 2.1.1, please upgrade immediately and do a full overwrite of your old files, especially those in wp-includes. Check out your friends blogs and if any of them are running 2.1.1 drop them a note and, if you can, pitch in and help them with the upgrade.
If you are a web host or network administrator, block access to “theme.php” and “feed.php”, and any query string with “ix=” or “iz=” in it. If you’re a customer at a web host, you may want to send them a note to let them know about this release and the above information.
Thanks to Ryan, Barry, Donncha, Mark, Michael, and Dougal for working through the night to figure out and address this problem, and thanks to Ivan Fratric for reporting it in the first place.
Questions and Answers
Because of the highly unusual nature of this event and release, we’ve set up an email address 21securityfaq@wordpress.org that you can email questions to, and we’ll be updating this entry with more information throughout the day.
Is version 2.0 affected?
No downloads were altered except 2.1.1, so if you’ve downloaded any version of 2.0 you should be fine.
What if we update from SVN?
Nothing in the Subversion repository was touched, so if you upgrade and maintain your blog via SVN there is no chance you downloaded the corrupted release file.
The above post is taken directly from wordpress.org. Spread the news and help others. Wordpress.org/download