Remembering faxes that when scanned actually containedalicious code embedded when converted into the digital format by the old school PTSN fax machines.

Warning description may be slightly off with how yhe fax machines and faxes were used as malware on corporate networks but I'm thinking it was back 2010-2016 time frame. So you can think your air gapped and then usb scan a picture printed from a fax machine and potentially still become infected or have your machine contain a bot it just won't reach the internet but should be scary AF for security researchers.

I think if we look at any spectrum for data transmission (abd I mean format not frequency spectrum specifically) but USB versions, RF transceivers or transmitters and receivers, old non-broadband, cellular infrastructures, network infrastructures built on current rj45 based and fiber networking all the way to satellite based and low frequency 900mhz up to 5 ghz and beyond all have some some weakness somewhere or can find a weakness in combination with other technology that device or system uses.

We have to work 10x harder than the hacker now especially people sell cryptolockers, private info and botnets on the dark web although I do think tor and .i2p are needed for people to feel safe online once they are more user friendly. At least firr .i2p where tor browser is user friendly but you gotta do your due diligence on dns potential vpns or multiple no log vpns etc. C hanging identities and randomized MAC IDs and dns and PGP encryption.