Does anyone know how to close the access point that is in most file sharing programs like limewire?

Having a file sharing program like Kazaa, Limewire, RocketPro, etc have an access point allowing hackers in. I read an article that the hole can be closed, but most computer users dont know how. Does anyone out there know how to make sure your file sharing program is not an open door to all? Does disconnecting your file sharing program and exiting the program after your done close the door or are there other options? Thanks!