Experimental malware has highlighted the possibility that hackers might be able to turn headphones into microphones in order to snoop on computer users.

Research by computer scientists at Ben-Gurion University, Israel, has revealed that both headphones and loudspeakers present a potential bugging risk. The boffins put together proof-of-concept malware, dubbed SPEAKE(a)R, in order to validate the risk.

"Malware can use a computer as an eavesdropping device, even when a microphone is not present, muted, taped or turned off," the researchers warn. In a paper, SPEAKE(a)R: Turn Speakers to Microphones for Fun and Profit (PDF), the researchers survey the scope of the risk and access potential countermeasures. Possible hardware-based defences include using only active one-way speakers or deploying either white noise emitters or an audio jammer.

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A speaker converts an electric signal into a sound wave. A microphone converts sound to an electrical signal. "The difference between these two pieces of equipment is that they have been optimised for the direction of conversion," according to Paul Farrington, manager of EMEA solution architects at application security firm Veracode. "However, there is little to prevent the conversion happening in the reverse direction."

This feature of consumer tech coupled with the possibility of hacking an audio port's role in the PC from output to input creates a bugging risk.

"The RealTek codec chip vulnerability is apparently allowing malware running on the device to take advantage of the physical properties of the connected equipment to use the ports to accept input when they should be restricted to output only," Farrington continued.

RealTek or operating system developers might be able to deliver a software patch to mitigate this chip vulnerability and help secure IO ports, according to Farrington. ®