Guaranteeing your anonymity is basically impossible if you use a mobile phone according to a new study.
Researchers say that a mobile user can be identified with as little as four pieces of location information.
Every phone sends data about its position and movement to mobile networks as soon as it's switched on, and this data is routinely handed over to third party companies.
Using four pieces of this data a user can be identified according to the study in Scientific Reports.
The research hinges on the predictability of human movement, which is far less unpredictable than we might like to think.
A team at the Massachusetts Institute of Technology (MIT) and the Catholic University of Louvain used 15 months of anonymous phone data for 1.5 million people.
They found that so-called "human mobility traces" are in fact highly unique.
In a set of data where location is updated hourly, with a relatively low resolution, a user can be indentified in 95% of cases.
"Even coarse datasets provide little anonymity," the researchers said - showing that in theory you don't have to give up much information to tell a third party a lot about who you are and where you go. Data like this is given up whenever you use WiFi or data with an app, call or text.
The BBC reports that mobility traces are even more unique than finger prints.
With just this data, third-parties would only be able to identify you as an individual - but not your name or other details. However in combination with Tweets, check-ins or other information it might be possible to build up a more complex picture.
A recently launched website was able to combine Instagram with location data to provide a map of people's homes, businesses and locations, for instance.
The researchers said:
"These results should inform future thinking in the collection, use, and protection of mobility data. Going forward, the importance of location data will only increase34 and knowing the bounds of individual's privacy will be crucial in the design of both future policies and information technologies."