“The attack, like all previous ones the researchers have devised for air-gapped machines, requires the targeted machine first be infected with malware—in this case, the researchers used proof-of-concept malware they created called Fansmitter, which manipulates the speed of a computer’s fans. Getting such malware onto air-gapped machines isn’t an insurmountable problem; real-world attacks like Stuxnet and Agent.btz have shown how sensitive air-gapped machines can be infected via USB drives.

To receive the sound signals emitted from the target machine, an attacker would also need to infect the smartphone of someone working near the machine using malware designed to detect and decode the sound signals as they’re transmitted and then send them to the attacker via SMS, Wi-Fi, or mobile data transfers. The receiver needs to be within eight meters or 26 feet of the targeted machine, so in secure environments where workers aren’t allowed to bring their smartphones, an attacker could instead infect an internet-connected machine that sits in the vicinity of the targeted machine.”

Source: Clever Attack Uses the Sound of a Computer’s Fan to Steal Data | WIRED