  It is possible to manipulate the headphones (or earphones) connected to a
computer, silently turning them into a pair of eavesdropping microphones - with
software alone. The same is also true for some types of loudspeakers. This
paper focuses on this threat in a cyber-security context. We present
SPEAKE(a)R, a software that can covertly turn the headphones connected to a PC
into a microphone. We present technical background and explain why most of PCs
and laptops are susceptible to this type of attack. We examine an attack
scenario in which malware can use a computer as an eavesdropping device, even
when a microphone is not present, muted, taped, or turned off. We measure the
signal quality and the effective distance, and survey the defensive
countermeasures.
