A system which is air-gapped is generally considered safe from intrusion as there are few network tunnels or avenues for hackers to exploit. After all, if you can’t connect, you can’t steal or tamper with air-gapped devices.
However, this idea has once again been smashed by researchers from Israel’s Ben Gurion University, who have demonstrated a method to steal information using the LED lights found on routers and switches used in isolated, secure networks.