Menstruation apps store excessive information
theguardian.com
theguardian.com
The link to the report. Quite interesting.
It's also troubling to me that large companies like apple want to make large scale "anonymized" health data collection common place and "normal". Citing "huge leaps in medical science" as a reason to start mass data reporting on their users.
Any effort you make to go from the latter to the former nets you a dollar less. This is especially true because accidentally collecting data is easy (you build in sync between devices or something).