Andrew -
My IE is version 11.0.9600.18163. I get regular Windows security updates (once a week) - but I do not update IE.
It appears those who have the most current IE have experienced the problem as well (Jeff says he gets it with Chrome, too).
Since this is about digital signatures, I assume this is simply some "disconnect" between Windows and PGMusic's signature process (most likely a Windows issue) and does not affect the file itself or have any bearing on the validity of the download other than something on this end saying "the signature is suspect - proceed at your own risk"...
Would you agree?
OK, I can duplicate that now. Turns out *my* IE wasn't totally up to date. Once I update to 11.0.9600.18163 I now get the same message as reported here. Our signature IS valid, so it is some kind of false positive - I have submitted a bug report to Microsoft.
For people who get this warning, you should click the 'View Downloads' button, then you can right-click on the downloaded file and select 'Run Anyways'.