Windows Defender is a free program that helps you stay productive by protecting your computer against pop-ups, slow performance and security threats caused by spyware and other potentially unwanted software. Windows Defender no longer supports Windows 2000 as mainstream support ended in June 2005. This is the most current release of Windows Defender. Note: This download is available to customers running genuine Microsoft Windows (Atleast from the Microsoft's Mirror)

Windows Defender x86 - Microsoft's Mirror
Windows Defender x64 - Microsoft's Mirror
Windows Defender x86 and x64 - 3rd Party Mirror