Can you stop an app connecting to the internet on a Mac?

Why it happens

The firewall built into macOS guards the way in: it decides which apps may accept connections from other computers. It doesn't watch traffic going out, so an app can still reach its servers even when it's blocked there. Fully stopping an app going online needs a separate outgoing firewall app.

How to fix it

1. Open System Settings, click Network, then Firewall, and switch Firewall on. Options stays greyed out until you do.

   Network›Firewall

2. Click Options. This list shows apps and the incoming connections they may accept.

   Network›Firewall›Options…

3. Click the + button, choose the app from Applications and click Add. Then set it to Block incoming connections and click OK.

4. For outgoing traffic, the simplest built-in step is to quit the app with Command-Q when you're not using it, or turn Wi-Fi off while it's open.

Still not fixed?

1. If the app keeps going online in the background, it may open by itself when you log in. Check General > Login Items & Extensions and remove it there.

   General›Login Items & Extensions

2. Block all incoming connections in Firewall Options shuts every app's way in, but it also stops sharing features such as AirDrop and Screen Sharing. Use it only if you need it.

3. If you need to block an app's outgoing traffic, you'll need a separate outgoing firewall app. Only install one from a developer you trust, as it sees all your network traffic.

4. If the Firewall switch is greyed out, your Mac may be managed by a school or company, so ask them. If it won't turn on at all on your own Mac, contact Apple Support.