Scientific American – The traces we leave on the Web and on our digital devices can give advertisers and others surprising, and sometimes disturbing, insights into our psychology

• Users’ digital footprints disclose certain preferences and characteristics, such as their personality or mood.
• Companies are very interested in such data. Automated language analysis is already being used in the hiring of personnel. And advertising seems to be more successful when its message is adapted to the personality or mood of the customer.
• These technological advances open opportunities not only for commerce but for public health. Among those possibilities: smartphone apps may in the future recognize when a bipolar patient is slipping into a depressive phase and can inform the person’s physician.
• But the technology poses risks. Unless it is managed carefully and ethically, it can invade privacy…”