Many of us talk on Skype, Hangouts, WhatsApp, or Viber while using the computer for something else. But have in mind that your conversation partner might find out what you are typing.

Click, click, click - almost every person talking on the phone or Skype knows that his or her conversation partner may be chatting or doing something else while conversing. The sound of typing on a physical computer keyboard is rather recognizable.

With help from machine learning and a computer it is possible to find out what your conversation partner is typing. Almost every keyboard has a slightly different sound for each key, which means you can use a recording of typing to find out which keys have been pressed. The accuracy is not perfect, but it is quite high nonetheless.

At the Black Hat hacking conference in Las Vegas, presentation showed how to make it happen. According to the researchers, even after the sound has undergone conversions during online transmission, the recordings of key clicks retain sufficient information to feed to a machine-learning system and get back the five most probable key presses. The results for the three test laptops that researchers used to conduct this study were different, but it was possible to retrieve the typed text even for the most "indistinctly clicking" Lenovo laptop.

This is where dictionary-based results come in. People generally type words that make sense; thus, any nonsense can be eliminated. It is enough to know which keyboard layout and language the victim probably used; the demonstration algorithm will deliver an intelligible and plausible result within a few seconds.

The experts claim that this technology might be used even to steal passwords, although that sounds a bit far-fetched. Passwords are too short and do not consist of real words most of the time.

The threat of "input interception" over Skype does not look too serious, but it's worth knowing about, especially if you sometimes deal with confidential information.

However, if you find yourself in a middle of an especially long and tiresome conference call, observe the golden rule: Anyone who is not speaking should mute his or her microphone until it's time to talk.