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Enabling Stealth Mode on OS X El Capitan

The most recent update to OS X El Capitan brought a very small, but very interesting change to the Firewall features included in OS X. This new feature is called “Stealth Mode” and is designed to give you significantly more protection when operating on public networks. With Stealth Mode turned on your computer will hide itself from network and port scans, and will not respond to attempts to gather intel about what services you are running. In essence, this makes your computer “invisible” to malicious actors who may be attempting to reconnoiter your system.

Activating this new feature is very easy, and is something that should be done whenever you are connecting to a public network. This can be accomplished by navigating to the Firewall options in System Preferences and clicking Firewall Options (System Preferences > Security & Privacy > Firewall > Firewall Options > Enable Stealth Mode).

firewall firewallOptions

This can also be accomplished through Terminal using the command:

/usr/libexec/ApplicationFirewall/socketfilterfw --setstealthmode on

and similarly turned off using the command:

/usr/libexec/ApplicationFirewall/socketfilterfw --setstealthmode on

Now keep in mind this is not necessarily something you want to leave turned on at all times. It is likely that this will interfere with many common home and business applications. For example, your system will no longer be discoverable for file or screen sharing by other devices on your network. So if, for example, your system only resides on a private network that is already behind a firewall, the cost in convenience may outweigh the added security.


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