Automattic has released a new security update for WordPress 3.1. You can view the changelog below:

Various security hardening by Alexander Concha.
Taxonomy query hardening by John Lamansky.
Prevent sniffing out user names of non-authors by using canonical redirects. Props Verónica Valeros.
Media security fixes by Richard Lundeen of Microsoft, Jesse Ou of Microsoft, and Microsoft Vulnerability Research.
Improves file upload security on hosts with dangerous security settings.
Cleans up old WordPress import files if the import does not finish.
Introduce “clickjacking” protection in modern browsers on admin and login pages.

To update, simply click the Update Now link on your dashboard or if you need to update multiple wordpress blogs all at once, check out my bash script.