List of Service Principal Names (SPNs) amongst AD Users

Here is a simple powershell script to list the service principal names 
among user accounts in a Windows domain.  Understanding why the SPNs 
exist and how they could be abused is important.  

$info = Get-ADUser -Filter * -Properties ServicePrincipalNames
ForEach ($user in $info) {
    $samAccountName = $user.SamAccountName
    If ($user.ServicePrincipalNames -ne $null) {
        ForEach ($spn in $user.ServicePrincipalNames) {
            "$($samAccountName) $spn"
        }
    }
}