A firewall won’t protect someone from physically accessing your computer from within your home. In order to restrict access to your computer at home it is a good idea to use the login and password features of your operating system. A firewall also won’t protect against:
a) Viruses – most firewalls are not configured with up-to-date virus definitions, so a firewall alone will not protect you from virus threats. For this reason, each computer on your home network should have a current version of antivirus software.
b) User error – Intruders often try to trick computer users into compromising their computer’s security. They may send false or enticing email messages to lure users into divulging sensitive information. In these cases, if permission is granted to others through the Internet, a firewall may not be able to prevent any resulting damage.