How Your Health Data Lead A Not-So-Secret Life Online

There are apps that can help people with diabetes keep track of their blood sugar and apps that can attach to a blood pressure cuff and store blood pressure information. I use an app called ZocDoc to schedule and manage doctor's appointments. Every time I see a therapist or a primary care doctor or dentist, the data get stored in my personal account.

But we leave behind other trails of health data, too, from apps and activities that are sometimes only tangentially health related. When I walk down the street, an app on my phone logs steps as it bounces against my thigh. When I swipe a loyalty card at the pharmacy, the over-the-counter medications that I buy become bits of data attached to my name. Medical information can be gleaned from all this and more, says Nathan Cortez, a professor of law at the Southern Methodist University Dedman School of Law.

Those data aren't always protected. A recent report from the Department of Health and Human Services showed that the vast majority of mobile health apps...