This release includes enhanced features that reflect ongoing input from customers, as well as Microsoft’s growing understanding of the spyware landscape.
To download the x64 version of Windows Defender Beta 2, click here.
Specific features of Windows Defender Beta 2 include:
- A redesigned and simplified user interface – Incorporating feedback from our customers, the Windows Defender UI has been redesigned to make common tasks easier to accomplish with a warning system that adapts alert levels according to the severity of a threat so that it is less intrusive overall, but still ensures the user does not miss the most urgent alerts.
- Improved detection and removal – Based on a new engine, Windows Defender is able to detect and remove more threats posed by spyware and other potentially unwanted software. Real Time Protection has also been enhanced to better monitor key points in the operating system for changes.
- Protection for all users – Windows Defender can be run by all users on a computer with or without administrative privileges. This ensures that all users on a computer are protected by Windows Defender.
- Support for 64-bit platforms, accessibility and localization - Windows Defender Beta 2 also adds support for accessibility and 64-bit platforms. Microsoft also plans to release German and Japanese localized versions of Windows Defender Beta 2 soon after the availability of the English versions. Use WindowsDefenderX64.msi for 64-bit platforms.
Source:
microsoft.com 
Windows® Defender (Beta 2) ver-1347 
