Software firewalls can be good at stopping attackers from gaining access to your system. Often though, they also stop you from accessing what you need to on the Internet.  For the most part the operating system (Microsoft Windows and Mac OS) are good enough to protect you from most external intrusions.  If you are still concerned then our recommendation is to install a hardware firewall router, either wireless or hard-wired, like a Linksys or D-Link router available at any computer store.