'There are 235 types of permissions on more than one million apps in the Google Play store'

US smartphone users are anxious to protect their private data, but it can be challenging in a massive system of applications with various policies and technical needs.

A study released Tuesday by the Pew Research Center found 235 types of permissions on more than one million apps in the Google Play Store.

The survey found smartphone users are keen to understand how their data is being used and shared: 60 per cent of people using the Play Store had decided against installing an app when they discovered how much personal information is required, and 43 per cent had uninstalled an app for the same reason.

Users need to accept terms when downloading an application.

But the study noted that "once that permission is granted, the apps can amass insights from the data collected by the apps on things such as the physical activities and movements of users, their browsing and media-use habits, their social media use and their personal networks, the photos and videos they shoot and share, and their core communications."

The researchers said 90 per cent of app downloaders indicated that how their personal data will be used is "very" or "somewhat" important to them when considering whether to download an app.

"The data suggest that users are concerned about the information that apps require, but less is known about what permissions these apps are most likely to ask for," said Pew research Aaron Smith.

App permission is not necessarily pernicious, the researchers said: a program may need to access the camera, flash or location in order to function properly.

But more troublesome is how personal data is accessed and shared with marketers or other parties.

Privacy depends on context

"Our research on privacy suggests that Americans' attitudes are highly contextual - users might be happy to share a particular piece of information in one context, but much more concerned about sharing it in a different context," said study author Kenneth Olmstead.

"Some of the most popular apps require their users to grant access to a wide range of potentially sensitive personal information - while at the same time, many apps request little to no information from their users but have been downloaded only a handful of times."

The research, focusing on Android applications and not Apple's iOS apps, which are on a more tightly guarded system, said a relatively small number of apps dominate the ecosystem.

It found 47 per cent of all apps available in the Google Play Store had been installed fewer than 500 times, while 11 apps were downloaded more than 500 million times.

The research underscored growing privacy concerns about smartphone applications and their ability to glean data from users.

A separate study last month by university researchers found 73 percent of Android apps shared personal information such as email addresses with third parties, and 47 per cent of iOS apps shared location data with third parties.

Apple has in some cases removed applications that share data with third parties without user permission.

But the researchers from the Massachusetts Institute of Technology, Harvard and Carnegie Mellon University said much of the sharing of data was not disclosed.

"Given the popularity of apps on smartphones, consumers worry about how much personal information apps share," they wrote in the Journal of Technology Science.

The Pew research found the average application asks for five permissions, with the most popular one simply accessing the connectivity of the smartphone.

The majority of the permissions related to allowing apps to access hardware functions of the device such as controlling the vibration function, while 70 allowed apps to access some kind of personal information.

The Pew study examined more than one million Android apps and interviewed 465 adults in January and February 2015. The margin of error was estimated at 5.8 percentage points.