Windows Defender

Windows Installer 3.1

I want to install Windows Defender on my desktop, but I always get an error message that I don't have Windows Installer 3.1. I have tried to install that, but to no avail. How do I go about installing the Installer 3.1?

Do you think Windows Defender is at least as good as Microsoft AntiSpyware ?

When Microsoft AntiSpyware was first released, I installed and used it for several months, and I was really satisfied with it, but I have the impression that after migrating to Windows Defender, the level of anti-spyware protection has lowered to the point that I felt the need to install another...