Yes, as a complete suprise it seems that Microsoft has released the final version of their long-time-in-the-making Anti-Spyware program, Windows Defender.
The build is marked as 1.1.1592.0 and it seems it can be installed over top previous versions (Beta 2, It can not be installed over top Beta 1 previously known as Microsoft Anti-Spyware Beta).
The only noticeable changes are the minor color scheme updates to the User Interface (Previously a Light Blue > Dark Blue gradient, now a Blue > Green gradient.) And as well a new option to display the System Tray Icon even when the program is not in the process of updating or scanning the computer. Other changes include more improvements to the scanning engine as well as an improved Software Explorer.
Windows Defender can be installed on both 64-Bit and 32-Bit versions of Windows XP / Windows Server 2003. However, unlike previous releases, Defender is no longer supported on the Windows 2000 platform. For Windows Vista users, well it seems you're left in the dark on this one. This build can not be installed on Vista and the integrated version can not be updated to the new version through the integrated updating engine.
Beta 2 users have until December 31st to upgrade to the final version before the program expires and ceases to function.
Download: Windows Defender Final 32-Bit
Download: Windows Defender Final 64-Bit