Summertop: Depends a bit on the terminology (and the type of modem). They do route in a certain way, but their primary purpose is to connect two different type networks (cable structure on one side, ethernet on the other). I'd consider it a router if it has its own TCP/IP stack. If it's just changing electronical signals (like old fashioned telephone modems do) I call it a modem. Whether or not it "offers protection" depends on what you mean by protection, and how it is configured. I don't use cable modems myself, but the ADSL modem I use at home can be configured to act as a NAT box, and to selectively let outside traffic through (firewall like functionality). However, I've set it up to be in "bridging" mode - it lets all traffic through. This might look less secure, but it isn't - it's more secure. In bridging mode, all traffic from the outside goes to my box - an attacker cannot target the modem, since, from the outside, it doesn't have an address. So if there's an exploit in the OS of the modem, my modem won't be effected. This of course means that my OS is subjectable to attacks, but my OS is open source, and I can freely and quickly apply patches. Or fix it myself if I'm really need to.