Data protection fears relating to the Google Dialer and Messages apps on Android phones have been highlighted in a new study by Trinity College Dublin.
Researchers found that the Messages app tells Google whenever a message is sent or received and that unique identifiers allow Google to discover whether two handsets are communicating, and at what times.
The Dialer app tells Google whenever a phone call is made or received.
The information sent includes the time and the call duration. This allows Google to discover whether two handsets are calling one another, and at what times and for how long.
According to the study, the information gathered allows a detailed picture of app usage over time to be reconstructed by Google.
Some of the data being sent may also include personal details.
There is no opt out from this data collection.
The apps are used to make and receive calls or to send and receive SMS and other messages and are pre-installed on many Android phones.
According to Google, more than one billion phones have both.
In the US, AT&T and T-Mobile recently announced that all Android phones on their networks will use the Google Messages app and the app also comes pre-loaded on Samsung, Xiaomi and Huawei handsets.
The study was carried out by Professor Doug Leith at the CONNECT SFI Research Centre for Future Networks at Trinity College Dublin.
"I was surprised to see such obviously sensitive data being collected by these Google apps. It's not at all clear what the data is being used for and the lack of an opt-out is extremely concerning," Professor Leith said.
The Trinity research team says it has been told by Google that, in light of the report's findings, it plans to make changes to the Google Messages and Dialer apps.
Google said it welcomed partnerships and feedback from academics and researchers, including those at Trinity College.
"We've worked constructively with that team to address their comments and will continue to do so," a Google spokesperson said.