We recently published a report with the University of New South
     Wales and the University of Berkeley has revealed that these apps
     are not as secure as they make out to be.
     The first analysis of its kind, the report looked at 283 Android VPN
     apps, investigating a wide range of security and privacy
     features.VPN facts from the study
     Alarmingly, the report uncovered that not only did 18 per cent of
     the apps fail to encrypt users’ traffic but 38 per cent injected
     malware or malvertising – software designed to damage or gain access
     to the users’ information. The very reason users install these apps
     – to protect their data – is the very function they are not
     performing and these apps have been installed by tens of millions of
     users.
     And what’s more, the report found that over 80 per cent of apps
     requested to access sensitive data such as user accounts and text
     messages.
     While most of the examined apps offer (some form of) online
     anonymity, some app developers deliberately sought to collect
     personal user information that could then be sold on to external
     partners.

   [1]https://blog.csiro.au/tinker-torrentor-streamer-spy-vpn-privacy-aler
   t/
   Also see: Flurry, The Company That Tracks More Phones Than Google Or
   Facebook” and you’ve probably never even heard of them.
   [2]http://auntieimperial.tumblr.com/post/65616918121

References

   1. https://blog.csiro.au/tinker-torrentor-streamer-spy-vpn-privacy-alert/
   2. http://auntieimperial.tumblr.com/post/65616918121