The Eclectic Light Company writes:
A few years ago, most Mac users had firewalls in their routers which blocked all incoming connections, and that was all they wanted. Over those years, we’ve increasingly installed software firewalls on our Macs to block outgoing connections. This article looks at some of the issues that arise from doing that.
The rules of the game keep changing, and this article brings us up-to-date.
Check It Out: All About Apps Phoning Home. And Firewalls