I am trying to remove this from my system using Add and Remove programs. When I attempt removal, I get a message that the program cannot find the WindowsDefender.msi file. File does not exist on my computer. Cannot download Windows Defender from Microsoft site, says that program already exists. Can I eliminate program by deleting file from Program Files and all references from registry? Or, any other help appreciated.

Thanks in advance.

Others have successfully used the Windows Installer Cleanup utility to uninstall Defender.
Description of the Windows Installer CleanUp Utility.

Are you using Defender in Vista? If so, you can only disable Defender. It is a feature of Vista and part of the operating system so you cannot uninstall it.

"How to Turn Windows Defender on or off in Vista"

T-Mack--Was successful in removing after using Windows Installer Cleanup Utility.
Thanks for the help.

Glad to hear
Your welcome.