I am an experienced computer user but I have had no experience of Networking. I have two laptops networked through a Linksys BEFSR41 router to a NTL cable modem. Everything works OK. What I do not under stand is the need for a firewall. I understand, well I think I understand, that the router has some form of built-in firewall. Is this sufficient or do I need extra protection? I have used search but I did not find an answer to my dilemma.