Thanks for posting. That looks like an important update.

From WordPress release.

WordPress 3.6.1 is also a security release for all previous WordPress versions and we strongly encourage you to update your sites immediately. It addresses three issues fixed by the WordPress security team:

Block unsafe PHP unserialization that could occur in limited situations and setups, which can lead to remote code execution. Reported by Tom Van Goethem.
Prevent a user with an Author role, using a specially crafted request, from being able to create a post “written by” another user. Reported by Anakorn Kyavatanakij.
Fix insufficient input validation that could result in redirecting or leading a user to another website. Reported by Dave Cummo, a Northrup Grumman subcontractor for the U.S. Centers for Disease Control and Prevention.

Additionally, we’ve adjusted security restrictions around file uploads to mitigate the potential for cross-site scripting.