EEG (electroencephalography) has been used by medical professionals for more than five decades. In this technique, electrodes are placed on the head and brain waves are recorded. This device was once very expensive and used only for medical applications, but it has recently been marketed for personal use. In these use cases, the brain waves are transferred to a computer and are used to control various computer functions.
Scientists have found that brain-wave sensing headsets put users at risk. For example, if you pause your game and log into your bank account, a hacker may use your brain waves to steal your passwords.
Source: Daily Mail Online