Network monitoring can be tricky, but here’s a free Macintosh OS X Lion application that can help.
Usually, a network monitor is used to monitor what network connections an application is using. For example, in the image above, you can see that iTunes is connecting to Akami, and has 10 connections open…
Obviously, this can be used to ensure that your applications are communicating with the services, and resources that you expect. But it can also be used to find out what faceless applications are hiding in the background, without your knowledge.