Should I use a firewall if I have more than one computer in a home or small-office network?
Yes. If you have more than one computer in a home or small-office network, you should protect every computer in the network. Turning on Windows Firewall or another firewall on every connection will help prevent the spread of a virus from one computer to another in your network if one of your computers becomes infected. However, if you open an infected email attachment, the firewall won't block it and it can infect your computer. You should install an antivirus program as well.