Microsoft has released Microsoft Security Essentials Prerelease

As a Microsoft Security Essentials Prerelease user, you will have the opportunity to explore and test new builds of Microsoft Security Essentials before they are publically available and provide feedback to Microsoft. Your feedback helps Microsoft to make its software and services the best that they can be. As a Microsoft Security Essentials Prerelease user, Microsoft Security Essentials updates will automatically be installed on your computer through Microsoft Updates. To help us improve the software, you will be enrolled in the Microsoft Error Reporting, Customer Experience Improvement Program, and Microsoft Active Protection Service. To learn more about these programs, see the Microsoft Security Essentials privacy statement at http://go.microsoft.com/fwlink/?LinkId=290997 .
Leaving the program: If you wish to leave the prerelease program at any point in time, you can do so by uninstalling the program from your computer.

IMPORTANT NOTE: If you wish to be able to submit feedback to Microsoft about this program you have to register to the Security Essentials Prerelease program on Microsoft Connect: http://go.microsoft.com/fwlink/?LinkId=254220.
By registering to the Connect program you will be able to submit feedback and receive notifications and announcements from Microsoft about this product. You will also need to be registered to the prerelease Connect program in order to view prerelease-specific content like a modified privacy statement for a specific prerelease version.

  Microsoft Security Essentials Prerelease