Sadly, there are many "snake oil" apps in the digital world.
A woman in Kenya had HIV misdiagnosed by a "prank" smartphone app--probably shared by Bluetooth, a common way in that part of the world. This unfortunate event highlights the danger of using unregulated health apps. In the U.S. there is a modicum of oversight by the FDA's most recent guidelines or Apple's more rigorous standards for this kind of app.
PositiveTip: Do some research before installing a medical app--no matter how alluring the promises. Doing this could spare you a lot of trouble.