Little Snitch informs you whenever a program attempts to establish an outgoing Internet connection. You can then choose to allow or deny this connection, or define a rule how to handle similar, future connection attempts. This reliably prevents private data from being sent out without your knowledge. Little Snitch runs inconspicuously in the background and it can also detect network related activity of viruses, trojans and other malware.

New in v3.6

Little Snitch 3.6 is ready for OS X El Capitan.
Added support for watchOS and tvOS simulator apps.
Other improvements and bugfixes.

Homepage - http://www.obdev.at/products/littlesnitch/index.html