Show warning message for User Logged in
I need to show one Popup window for ,
If the user logged in one portal( as user id: xxxxxx, pwd:yyyyyy), in the mean while another user is logging to the same portal( as user id: xxxxxx, pwd:yyyyyy), the popup window shows to the Second user that
"the User have been logged Already"
Whether any default features are there in portal or need to customize using API?