The optional firewall settings let you control whether signed applications are automatically allowed through the firewall, control the list of allowed (or denied) applications, and enable stealth mode (which means your Mac won't respond to any unsolicited connections).

The four system resource domains are:

• User, containing applications and system resources specific to each user account

• Local, containing applications and system resources available to all users on the local Mac

• Network (optional), containing applications and system resources available to any Mac that has an automated network share

• System, containing applications and system resources required to provide basic

General application troubleshooting steps include restarting the application, trying another known working document, trying another user account, checking log files, deleting cache files, replacing preference files, and replacing application resources.

Gatekeeper can restrict software to Mac App Store applications only, or Mac App Store and identified developer applications only (this is the default option), or any application regardless of origin.