It's in the message you get from Windows advising you that it thinks the program is not what it says it is. It's been a while since I've downloaded and installed it. but I think after the text of the warning, it says something like "More", or "Install any way" At any rate don't abort the installation, click whatever it is that lets the installation continue.
Well, I tried installing it on my computer and it went without any of the messages, so I can't provide a better explanation. I know, and have experienced what you have, I guess that once a version is "approved" by the computer operator it remembers it when it's reinstalled.