Restrict Multiple Logins in Domain (AD)

I have always asked this question to my colleagues as to "How do i restrict Multiple Logins in an Active Directory Setup"

So here is the answer

Create a file when a user login and check for such file each time the login request is received  if file exists logoff, if file is not present Login and create the file. Its that simple

Below is the step by step process to achieve this using Group Policy

Assumptions: