, ▁using ▁FM ▁frequency ▁signals . ▁ ▁In ▁ 2 0 1 5 , ▁" Bit Wh is per ", ▁a ▁cover t ▁signal ing ▁channel ▁between ▁air - g apped ▁computers ▁using ▁thermal ▁manip ulations ▁was ▁introduced . ▁" Bit Wh is per " ▁supports ▁bid irection al ▁communication ▁and ▁requires ▁no ▁additional ▁dedicated ▁peri pher al ▁hardware . ▁ ▁Later ▁in ▁ 2 0 1 5 , ▁research ers ▁introduced ▁" GS Mem ", ▁a ▁method ▁for ▁ex fil tr ating ▁data ▁from ▁air - g apped ▁computers ▁over ▁cell ular ▁frequencies . ▁The ▁transmission ▁- ▁generated ▁by ▁a ▁standard ▁internal ▁bus ▁- ▁rend ers ▁the ▁computer ▁into ▁a ▁small ▁cell ular ▁transmit ter ▁anten na . ▁ ▁In ▁ 2 0 1 6 , ▁research ers ▁categor ized ▁various ▁" out - of - band ▁cover t ▁channels " ▁( O OB - CC s ), ▁which ▁are ▁mal ware ▁communication ▁channels ▁that ▁require ▁no ▁special ized ▁hardware ▁at ▁the ▁transmit ter ▁or ▁receiver . ▁O OB - CC s ▁are ▁not ▁as ▁high - band width ▁as ▁conventional ▁radio - fre quency ▁channels ; ▁however , ▁they ▁are ▁capable ▁of ▁le aking ▁sensitive ▁information ▁that ▁require ▁low ▁data ▁rates ▁to ▁communicate ▁( e . g ., ▁text , ▁recorded ▁audio , ▁crypt ographic ▁key ▁material ). ▁ ▁In ▁general , ▁research ers ▁demonstrated ▁that ▁air - g ap ▁cover t ▁channels ▁can ▁be ▁realized ▁over ▁a ▁number ▁of ▁different ▁medium s , ▁including : ▁ ▁ac oust ic ▁