This is the official guide for the Mac application Little Snitch.
A firewall protects your computer against unwanted guests from the Internet. Little Snitch protects your private data from being sent out.
As soon as you’re connected to the Internet, applications can potentially send whatever information they want to wherever they want. Sometimes they do this for good reason, on your explicit request. But often they don’t. Little Snitch allows you to intercept these unwanted connection attempts, and lets you decide how to proceed.
This guide will help you understand the basic concepts of network communication and provide help to leverage Little Snitch's rich functionality.