Last week, there were allegations that Facebook was eavesdropping on the conversations of users through the microphones of mobile devices. The social network, which denied the claims, was said to use the information that it acquired through this practice to serve better targeted advertisements.

The theories may have led some users to disable microphone access for the Facebook app on their mobile phone. A new research, however, shows that there is at least one other way for others to spy on users.

The VibraPhone research, by associate professor Romit Roy Choudhury and PhD candidate Nirupam Roy from the University of Illinois at Urbana-Champaign's Electrical and Computer Engineering school, claims that the vibration motor of smartphones can also be used to eavesdrop on users.

The vibration motor is a very small speaker that is included in smartphones. Every speaker, however, by changing the direction of voltage, can also function as a microphone, and this possibility is the focus of Choudhury and Roy's research.

It should be noted, however, that the attack is not simple at all to execute. For those who would attempt to use the vibration motor of a smartphone to listen in on the conversation of certain targets, they would first have to acquire the device and physically rewire the vibration motor. There is also the possibility that the process can be done in a less invasive way by exploiting the power controller chip of the device, but that route was not investigated by the researchers.

Once the rewiring is done, the vibration motor will be able to collect voltage variations that can be reconstructed into waveforms. However, in what is another limitation to the attack, the recorded sounds are difficult to understand, as the captured frequencies are only up until 2 kHz.

As such, users that are still wary of the possible eavesdropping would have to speak in high-pitched voices, and the stares that would come the person's way is generally not worth it considering the fact that the attack is very difficult to implement.

The paper will be presented later this month in Singapore at the annual MobiSys conference.