http://www.microsoft.com/downloads/details.aspx?familyid=435bfce7-da2b-4a6a-afa4-f7f14e605a0d&displaylang=en

  Specific features of Windows Defender 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 supports accessibility and 64-bit platforms. Microsoft will release localized versions including German and Japanese soon after the availability of the English versions. Please be sure to use WindowsDefenderX64.msi for 64-bit platforms.
  


• Delta definition updates - Windows Defender now downloads smaller delta definition updates when possible which reduces the time required to download and install definition updates. Customers can expect shorter download times when updating their definition updates.
  


• Free Limited Support - As a part of our commitment to the security of our customers, free support for installation, configuration, definition update, detection and removal errors will be available for a limited time after download and installation. Please refer to the Windows Defender support policy for more information.
  


• WGA enforcement - There are significant risks to running non-genuine Windows. Only genuine Windows customers can receive product downloads, Windows updates and special offers. Windows Defender will validate that your copy of Windows is genuine before installation. Furthermore, Windows Defender will only remove Severe threats for machines that are not genuine. Low, Medium and High threats will be detected, but not removed unless your copy of Windows is genuine. For more information, please visit http://www.microsoft.com/genuine
  

Important Notes

• Windows Defender no longer supports Windows 2000 as it will be out of mainstream support in October 2006. Please refer to the support lifecycle website for more information.