Yes, I thought about it, for example we entered login to Yahoo messenger in one computer A, if we go by logging elsewhere in computer B, then log on automatically to a computer A closed. (I wanted to like this)
I think, if the IP address block does not help because when the username and password in the know people, they can easily enter the login.
I created a website which sells a special article for the company, which the company is a lot of people who want to read and they have to get membership. Then if the company becomes membership and username given to someone, then someone else in the company is no longer a membership again. The potential customer is reduced.
I think it is useful to others in my case. Maybe there someone can help. Thank you.