A friend of mine has a cable modem/wireless router setup in his house. His two daughters each have their own PC with wireless USB adapters so they can access the internet; they do not share files or printers with each other or with their Dad. He has a concern that malware they may pick up on their PCs might be able to find its way to his PC. I don't know a lot about this topic, but such an occurrence doesn't seem likely to me. Is there a chance of this happening?