SharePoint 2010 Login Issue

We are having 7 server front-end farm with 2 SQL Server Failover SQL Server. our SharePoint is configured with Mixed Mode (i.e. Form Based Authentication and Domain Authentication). Our company employee will authenticate by domain account and Internet user will authenticate by form based. 

We have some kind of subscription on SharePoint which Internet user can buy on SharePoint and on their account provide some kind of access. As now subscription and access is involved.

I am looking that if user is logged in from machine or 1 browser, same user should not be able to login from other machine or different. IF he wants then we can remotely log off from other PC than only he can login from new PC.

So can somebody tells me how can achieve this by code or some kind of settings.