Recently I had to download some windows 8 consumer preview drivers for my Samsung Series 7 Slate. But when a file is downloaded from the web, Windows tags those files (if its an archive, it tags the files inside that archive as well) with a security attribute to ‘block’ execution of those files. Previous windows versions allowed unblocking via the File Properties property window. In Windows 8 Consumer Preview, it looks like its missing from the explorer ribbon! So the recourse is to use powershell cmdlet to unblock the file as follows.

1. Launch Windows Powershell (type powershell on the start screen, it comes bundled in Windows 8)
2. Type “Unblock-File <<file_to_unblock.extn>>”
   (you can type unb and press tab to autocomplete the cmdlet, and the first few chars of the filename and tab to autocomplete that too)
3. A successful execution of the cmdlet shows no message.

If you need more info on the Unblock-File cmdlet, type “Get-Help Unblock-File” for the details on what arguments it accepts. Also available here.