WordPress has issued an urgent upgrade for users who downloaded WordPress 2.1.1 within the past 3-4 days:

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.

This is the kind of thing you pray never happens, but it did and now we’re dealing with it as best we can.