Secure and Sanitized Code Guide

Can you explain best practices for writing secure and sanitize given {Language:PowerShell} code? How can I ensure that my code is secure and protected against malicious attacks? Code: 
{Code:function Get-AtomVersion {     param (         [xml]$FeedContent     )      # Check for Atom version 1.0     if ($FeedContent.feed.'@xmlns' -eq "http://www.w3.org/2005/Atom") {         return "Atom 1.0"     }      return "Unknown" }}