This evening the WordPress team have released version 3.1.2 for immediate download. This is a security update so you are advised to update to it as soon as possible to keep you blog safe and secure.
Here is the announcement from the official WordPress site:
WordPress 3.1.2 is now available and is a security release for all previous WordPress versions.
This release addresses a vulnerability that allowed Contributor-level users to improperly publish posts.
The issue was discovered by a member of our security team, wordpress developer Andrew Nacin, with Benjamin Balter.
We suggest you update to 3.1.2 promptly, especially if you allow users to register as contributors or if you have untrusted
You can download the security update or you an update from the dashboard of your blog admin panel.