Using Mac OS X's Built-in Firewall - dummies

Objective-See: LuLu Yes! Apple's built-in firewall only blocks incoming connections. LuLu is designed to detect and block outgoing connections, such as those generated by malware when the malware attempts to connect to it's command & control server for tasking, or exfiltrates data. Can Macs Get Viruses & Do Macs Need Antivirus Software However, the menace right now appears to be adware and potentially unwanted programs (PUPs), according to Malwarebytes who suggest that: "macOS’ built-in security systems have not cracked down Built-in Firewall blocking VNC connections - Apple Community Nov 27, 2016 Mac - Apple

The only problem I encountered with this method is that the defaults command tends to change the ownership of the com.apple.sharing.firewall file from -rw-r--r-- root admin, which also disables the firewall. Changing the permissions back and rebooting will reactivate the built-in firewall.

May 09, 2020 Best Free Firewalls for PC and Mac Jan 31, 2014

The only problem I encountered with this method is that the defaults command tends to change the ownership of the com.apple.sharing.firewall file from -rw-r--r-- root admin, which also disables the firewall. Changing the permissions back and rebooting will reactivate the built-in firewall.

Tap Firewall Options, and you can choose which apps can receive inbound connections and even enable a Stealth Mode, which will make your Mac less visible on public networks by preventing it