If you’ve ever found the Significant Locations section on your iPhone, then a recently published study that shows how such data can be used to decipher personal information about users should pose some alarm.
The way Significant Locations works is that your iPhone keeps a list of places you frequently visit. This list usually shows your favorite places and shops and will, of course, log the location of any service you might visit often, such as the medical center.
Apple gathers this information to provide “useful location-related information” in its apps and services, and promises this data is encrypted and cannot be read by Apple. But I’m a little unclear whether this information is made available to third-party apps.