Hi there,
Since your product is hosted on other sites, would be very helpful to provide MD5, SHA1 hashes on your website.
The good place would be your page where download links are.
The easiest way to generate and check hashes is to use free 'Microsoft File Checksum Integrity Verifier utility'
http://support.microsoft.com/kb/841290
command line usage: fciv.exe filename.exe
Thanks.