If you’ve recently upgraded your WordPress install to version 2.1.1 make sure that you upgrade to 2.1.2 immediately.

Long story short: 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.

From: http://wordpress.org/development/2007/03/upgrade-212/

Head over to the official WordPress blog to get the full story.