HT5318: About the security content of iTunes 10.6.3Learn about About the security content of iTunes 10.6.3
Currently Being ModeratedSep 23, 2012 11:24 AM (in response to libertysnoopy)
That suggests the installer is getting damaged during the download.
I'd first try downloading an installer from the Apple website using a different web browser:
If you use Firefox instead of IE for the download (or vice versa), do you get a working installer?