How to re-install Windows Installer:
http://xphelpandsupport.mvps.org/how..._windows_i.htm

Also:
Common Windows Installer Problems
http://support.microsoft.com/?kbid=555175

JS

"Robert S" <robert_s@emailme.net.au> wrote in message
news:uGZfJRjHHHA.1816@TK2MSFTNGP06.phx.gbl...
> If I try to install the latest windows defender the verification works OK
> but I get a message when I run the .msi file: "This installation package
> could not be opened. Contact the application vendor to verify that this
> is a valid Windows Installer package".
>
> How can I fix this?