Internet Firewall - a traditional firewall is a device (either a computer running Windows with firewall software installed, or a dedicated computing device running a non-Windows operating system and firewall software) that protects all the computers on a network from attacks by Internet criminals.

Personal firewall - software installed on each computer on the network that blocks intruders and attackers, either on the same network or another network (such as the Internet), from connecting to the computer.

All networks connected to the Internet need a firewall of some kind. Home networks can use simple "broadband routers" that have basic firewall features. If you run a business network and have valuable information stored on your network, you should investigate powerful firewalls that provide more protection and services, such as Microsoft's ISA Server 2000.

Personal firewalls should be used on all computers that have a direct connection to the Internet. For example, if you have a modem connected to your Windows XP computer, you should have either the Internet Connection Firewall (ICF) enabled (ICF is included with Windows XP - you don't have to buy it) or if you're extra paranoid, you can buy a more full featured personal firewall.

If your computer connects to the Internet indirectly (your computer is on a network that is protected by an Internet firewall), then the personal firewall is optional and in some cases should not be run because it might create conflicts.