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.
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.