In a previous post I mentioned how you could use the SysInternals streams utility to unblock files that were downloaded from the Internet.
Per that post: When you download a file from the Internet it gets tagged with an additional "NTFS Stream" of information — specifically with a Zone.Identifier record that tells Vista that the file came from the Internet.
If you look at the properties of the file, you see a message: "This file came from another computer and might be blocked to help protect this computer." and there’s an Unblock button you can push that is supposed to remove the Zone.Identifier.
If you had downloaded a .zip file from the Internet and then extracted it, all of the files extracted would all show as blocked.
To quickly unblock every file in every sub-folder, use this PowerShell command:
Get-Childitem -Path ‘C:\PathToYourFolderHere\’ -Recurse | Unblock-File -Confirm:$false -Verbose