The "ISO" is actually a slideshow or a PDF file. When you open it, you see a text file saying: "Congratulations! To download the real Windows 10, complete 15 surveys and download our speed booster toolbar!" The malware here is the toolbar and the spyware that comes with the survey redirects.
You download win10_mini.iso (10.2 MB). You mount it or burn it to a USB. You click Setup.exe . Nothing appears to happen—or a fake error message says "Installation Failed: Missing DLL." windows 10 iso highly compressed 10mb