Firewall, a technological barrier designed to prevent unauthorized or unwanted communications between sections of a computer network. Source http://en.wikipedia.org/wiki/Firewall. A personal computer connected to the Internet without a firewall can be hijacked and added to an Internet outlaw's botnet in just a few minutes. A firewall can block malware that could otherwise scan your computer for vulnerabilities and then try to break in at a weak point. The only way to make a home computer 100% secure is to turn it off or disconnect it from the Internet. The real issue is how to make one 99.9% secure when it is connected. At a minimum, home computers need to have personal firewall and anti-malware software installed and kept up-to-date to find and remove viruses, spyware, Trojans and other malware. A home network that uses a wired or wireless router with firewall features provides additional protection. Source http://www.firewallguide.com/