The adi-osc-2016_R1-setup.exe that you have on your download site seems corrupt. The signature on the EXE is either corrupt or invalid.
There is a new version of IIO-Oscilloscope (recently added) which is has a valid digital signature.
IIO Oscilloscope [Analog Devices Wiki]
The old installers were signed at the time they were created but their certificates are no longer valid today.
Just to add more info, this is due to Microsoft dropping support for SHA-1 signatures after 1/1/2016 due to security reasons assuming you're running Windows 10 (see the MS signing deprecation timeline and info).
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