It doesn't matter if you are using single or networked computer, if you are connected to internet then you need firewall protection to prevent hacking, virus, or any other security risks that might came from external. There are firewall hardware and software to prevent unauthorized access to your computer that connected to the Internet.
Firewall protection can be implemented into single or networked computer. Firewall working closely with a router program examines incoming and outgoing message, preventing intrusion from unknown sources.
Firewall techniques such as packet filter, application gateway, circuit level gateway and proxy server firewall. Firewall protection is important so that you can use the internet without much worry.