Guess, the idea that airgapped systems are secure has come to an end. The only way you can secure them is by using disposable thumb drives/CDs that only connect to the airgapped systems that the administrators setup. Even if the thumbdrive is connected to random machine once, you can assume that your airgapped systems are compromised. Very interesting stuff.
REFERENCES: Mordechai Guri, Boris Zadov, Dima Bykhovsky, Yuval Elovici, “PowerHammer: Exfiltrating Data from Air-Gapped Computers through Power Lines” in Cryptography and Security. April, 2018.