Hardening systems and environments
In the end, you can harden PowerShell as much as you like; if the systems on which PowerShell is running are not protected, adversaries will make use of that if they have the chance. Therefore, it is important to also look at how you can harden the security of your infrastructure.
Security baselines
A great start to hardening your Windows systems – regardless of the server, domain controller, or client – are the so-called security baselines provided by Microsoft. These security baselines are part of Microsoft’s Security Compliance Toolkit (SCT) 1.0, which can be downloaded from here: https://www.microsoft.com/en-us/download/details.aspx?id=55319.
Please be careful when applying security baselines!
You should never just apply a security baseline to a running production system. Before applying it, carefully audit your settings and evaluate them. Then, work on a plan to enroll your changes. Many settings are included...