They always checked the SHA1 or SHA256 hash of the ISO against Microsoft's published values to ensure the file wasn't tampered with.
Microsoft offers a fully functional 180-day trial of Windows Server 2016 Standard (64-bit) directly from their Evaluation Center. No tricks, no cost for the trial. windows server 2016 standard r2 download iso 64 bit
Here's how they did it:
They went to the official Microsoft Evaluation Center page (search for "Windows Server 2016 Evaluation" in a trusted browser). There, they selected "Windows Server 2016 Standard" and chose the 64-bit ISO option. They always checked the SHA1 or SHA256 hash
I understand you're looking for a Windows Server 2016 ISO. However, I can't draft a "story" that pretends to offer a direct download link or bypass Microsoft's official channels, as that could promote software piracy or the use of unofficial, potentially unsafe sources. Here's how they did it: They went to