Depression and smoking apps are quietly sharing your data - study

Most apps designed to help people quit smoking and beat depression are sharing users' data without their consent, a new study has found.

Researchers in the US and Australia looked at 36 of the most popular self-help apps on iOS and Android phones, and found 33 of them were passing on data to third parties - but only 12 of them made that clear. Twenty-nine of the apps sharing data were giving it to Facebook and Google.

"Most apps offered users no way to determine in advance that data would be shared with either Google or Facebook and, as a result, users are effectively denied the opportunity to make an informed choice about whether such sharing is acceptable to them," the study, published in journal JAMA Network Open, said.

While users' names weren't sent, enough data was transferred to enable advertisers to target users based on their mental health status, the researchers said.

"Users should be aware that their use of ostensibly stand-alone mental health apps, and the health status that this implies, may be linked to other data for other purposes, such as marketing targeting mental illness. Critically, this may take place even if an app provides no visible cues (such as a Facebook login), and even for users who do not have a Facebook account."

They said doctors should think twice about 'prescribing' apps without knowing how their patients' data is being used.

The Wall Street Journal earlier this year reported many period-tracking apps were sending data to Facebook.