They say good fences make good neighbors, and what goes for backyards may be even truer online. For most of us, using a Mac means that we don’t have to worry about intrusive computer viruses. But the internet is a big place, full of all sorts of evils looking for vulnerable computers, and a firewall can help keep your Mac secure. Here’s the lowdown on what a firewall is, how it works, and how to set up the one that’s already on your computer (trust us, it’s way easier than you think). We’ve also looked at some third-party firewall applications that offer features, flexibility, and protection that OS X alone can’t match. With the right software in place, you’ll be browsing, sharing, and surfing more safely in no time.