One of the new features of Windows Vista is the 
inclusion of Windows Defender, Microsoft’s anti-spyware security application that monitors files in realtime. While not automatically included, Microsoft has made Windows Defender available to Windows XP users, as well. The program’s abilities are limited to spyware/malware detection only, but offer an increased security shield when run alongside a full antivirus application like AVG Free (most anti-virus applications have lackluster spyware detection).
Download Windows Defender for Windows XP
