Multiple login

Hello everyone.
How to prevent multiple users login to one account?

you can change the code in customer controller login action method
by checking whether the customer is already logged in by using

var loggedincustomer=_authenticationService.GetAuthenticatedCustomer();
if(loggedincustomer==null || loggedincustomer.Email!=model.Email)
_authenticationService.SignIn(customer, model.RememberMe);