A powerful cybersnooping tool that can build an intimate personal profile of an e-mail user in seconds is in the spotlight after whistle-blower Edward Snowden's revelations about the US National Security Agency's international surveillance programme.
Immersion, developed by a trio of computing experts at the Massachusetts Institute of Technology's Media Lab, uses the same techniques as the NSA's global Prism programme to extract metadata - literally data about data - behind users' accounts.
With access to e-mails - but without reading the messages or subject lines - it can see how a user's life has changed from who is sending and receiving, when messages are sent and how that defines the networks and connections of an individual.
It demonstrates the potential ramifications of national security agencies seeking the same information about an individual.
The project led by 33-year-old Cesar Hidalgo, an assistant professor of media arts and sciences at MIT, was initially set up to explore a new way to display e-mails.
With the help of graduate students Daniel Smilkov and Deepak Jagdish, both 26, it eventually presented the team with an effective surveillance technique.
Smilkov said a side effect of focusing on e-mails was that it revealed much more intimate data and private information about users.
"From a privacy perspective it is powerful because you can immediately learn about your social network or you can see other personal data," he said, explaining that e-mails held more value than social networking sites such as Twitter and Facebook.
It also provides instant analysis. "You can immediately learn how that person is connected or the core groups that person is in," Smilkov said.
Immersion started last September, nine months before surveillance programmes became public knowledge.
Smilkov said the NSA had never entered his mind when the project was floated.
"So it kind of turned out to be a surprising side effect because they use the same metadata," he said. "We couldn't have wished for better timing."
He described his own experience of e-mail trawling as "personal and overwhelming".
But Smilkov believes the algorithms behind the Immersion tool have barely scratched the surface. The team now plans to explore the metadata behind Facebook and Twitter users.