Today I downloaded an update to our mail server on my dev machine using IE9 on Win7 Pro. I directed IE to save the file on our server's shared drive so I could install it later. When the download finished, IE showed a red banner at the bottom and said that, ".exe is not commonly downloaded and could harm your computer." There were three buttons, "Delete", "Actions", and "View downloads". I selected "Actions" just because I had never seen this before. It showed a "SmartScreen Filter" dialog basically giving three choices: "Don't run this program (recommended)", "Delete program", and "Run anyway". I just canceled the dialog because I didn't want to run it in the first place; I just wanted to download it so I could run it later on the server.
So when I did try to run it, it would blow up immediately saying, "Setup was unable to create the directory - Error 5: Access is denied." I tried unblocking the file, "Run as Administrator" even though I already was Administrator, turning off UAC, etc. Cutting to the chase, I finally downloaded the file again, ran WinMerge on the two and it showed they were identical, except the new one ran fine. I went back to my dev machine, downloaded the file through Firefox and then ran it on the server, again fine. But when I tried again through IE, again SmartScreen showed its red banner and somehow clobbered the file even though it was stored on another machine, and WinMerge can't tell the difference between it and a good file.
I've looked around on the web for how SmartScreen works, but they all give user-level descriptions of it. What I want to know is, what does it do to that file to make it unrunnable on another machine?