American researchers say they were shocked by how much information they were able to unearth about people by simply looking at the phone numbers they called.
The Stanford University study encouraged volunteers to install a tracking application called MetaPhone onto their phones.
Researchers collected information for several months, and say they were able to predict people’s medical conditions, hobbies and relationships by only looking at the metadata.
Graduate student Jonathan Mayer, who led the study, says the results show a significant amount of personal information can be discovered through metadata.
“One of the things which is most concerning about the privacy properties we’ve uncovered is how easy it is to make inferences about the metadata on a large scale,” he said.
“We had a participant who… had calls with a lumber yard and a locksmith and a hydroponics dealer and a bong shop.
“[You] don’t need a PHD in computer science to have some sense of what could be going on there.”
Mr Mayer says his team’s original hypothesis was that with only a few months of collection data and only a handful of users, the metadata would not be very revealing.
But he says he was surprised.
“For some individuals, the fact that they have a particular medical condition is quite private, for others are the fact that they own a gun is quite private,” he said.
“For others, their religious beliefs are quite private. And yet we were able to find many of these sorts of traits using just telephone metadata.”
MetaPhone study gathered same data as NSA
MetaPhone has been described as a slimmed-down version of the United States National Security Agency (NSA), because it has been collecting the same type of data which is collected by intelligence organisations.
Last year, documents from former NSA-contractor Edward Snowden showed Australia’s intelligence organisations had offered to provide raw metadata to overseas allies.
But often in the electronic surveillance debate, a distinction is made between what you say versus the metadata.
“The material that I understand was referred to in the Guardian story related to essentially the billing data, now that has been available – but there is a big difference between billing data and the actual content of calls,” Prime Minister Tony Abbott said in December, when asked about the Snowden leaks.