Restricted. This default execution policy applies to all Windows versions, with the exception of Windows Server 2012 R2. Restricted is the most secure policy because it allows PowerShell to operate only in an interactive mode. This means that you can only run individual commands. You can't run scripts under this policy, regardless of where the scripts came from (local or downloaded) and whether they're signed.
AllSigned. The AllSigned policy allows scripts to be run as long as they've been digitally signed by a trusted publisher. With this policy, when you attempt to run a signed script, you'll receive a prompt asking you to confirm that you trust the publisher.
RemoteSigned. The RemoteSigned policy allows scripts to be run but requires that downloaded scripts have a digital signature from a trusted publisher. Scripts that you run from the local computer don't need to be signed. Under this policy, there are no prompts when you attempt to run a script. RemoteSigned is the default execution policy in Server 2012 R2
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Unrestricted. The Unrestricted policy allows all scripts to be run, regardless of whether they're signed and where they come from.