When you have dial up internet service, your IP address changes all the time. It is difficult for someone that is looking to break into your computer to find you. When you cable or DSL your IP address will remain the same for several days, until your internet provider forces you to change, this is called a dynamic IP address. You should have a firewall of some kind (software or hardware) if you have a continuous connection to the internet. Websites have static IP addresses, costs more and they never change, so they are easy to find. But anyone with a website should have a firewall.