Good for some general perspective on (lack of) user privacy in the app industry:
http://techscience.org/a/2015103001/ "Who Knows What About Me? A Survey of Behind the Scenes Personal Data Sharing to Third Parties by Mobile Apps"
summarized by Ars Technica here: http://arstechnica.com/security/2015/11/user-data-plundering-by-android-and-...
"Apps in both Google Play and the Apple App Store frequently send users' highly personal information to third parties, often with little or no notice, according to recently published research that studied 110 apps. ... 49 percent of Android apps sent users' names, 33 percent transmitted users' current GPS coordinates, 25 percent sent addresses, and 24 percent sent a phone's IMEI or other details. An app from Drugs.com, meanwhile, sent the medical search terms "herpes" and "interferon" to five domains, including doubleclick.net, googlesyndication.com, intellitxt.com, quantserve.com, and scorecardresearch.com ..."
The Wikipedia apps were not among those tested - sadly, because it might have been a nice opportunity to highlight the fact that we don't share data with third parties at all. (In another context, we made that point with this tweet: https://twitter.com/Wikipedia/status/579220963755044864 )