Little Snitch will show you every connection attempt computers. This allows you to control all the data. This article is how to bring Little Snitch management rules in Network Monitor.
How to open Network Monitor?
Little Snitch click the icon in the status menu, and select "Display Network Monitor."
How to manage rules in Network Monitor?
You can click the icon to create rules and management rules.
Color icons indicate these rules apply to the entire application. In this example, all connections between Pages have been rejected.
Gray icons tell you that this application have more specific rules, some only allow or deny the connection. Calendar only allowed to connect to google.com.