I use Internet Connection Sharing in my home network—which computers must have a firewall?

All computers in your home network should be protected by a firewall. A firewall helps to prevent the spread of viruses or worms across your network if they infect one computer. A computer on the network could also become infected through a separate Internet connection, such as a laptop that is used on your home network and on public networks. Or, a virus could be introduced to a computer on your network through software installed from a CD or floppy disk.