This is the most current release of Windows Defender.
Windows Defender features
• New option to display Windows Defender system tray icon even when there are no pending actions needed.
• Enhanced performance through a new scanning engine.
• Streamlined, simplified user interface and alerts.
• Improved control over programs on your computer with enhanced Software Explorer.
• Multiple language support with globalization and localization features.
• Protection features for all users, whether or not they have administrator rights on the computer.
• Support for assistive technology for individuals who have physical or cognitive difficulties, impairments, and disabilities.
• Support for Microsoft Windows XP Professional x64 Edition.
• Automatic cleaning according to your settings during regularly scheduled scans.
Microsoft encourages all Windows Defender (Beta 2) users to download and install Windows Defender.