This type of file could harm your computer

I am developing a PHP web application in Apache server and it seems to work well with all major browsers even IE8. The only problem is with IE9. Basically my application lets users download a 30 day trial which is an exe file. At the download prompt, the dialog says "This type of file could harm your computer".

Some websites like red-gate.com and microsoft.com allows downloading of exe files but without this warning in IE9. What am I missing here?? I have some possible causes for this problem:

1. Is this specific only to Apache hosted w开发者_如何学运维ebsites? Its because red-gate and microsoft.com are hosted in IIS/ASP.NET platform.

2. The exe file is not digitally signed?

3. Or this is simply a bug in IE9?

I would like the message "This type of file could harm your computer" to be completely remove when users are downloading the exe files using IE9. Any thoughts?

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It looks like the content-disposition header is the key. See http://support.microsoft.com/kb/2566263