Smartphones leak far more personal information about their users than previously imagined, according to new research.

Security researchers at Sensepost were able to track and profile punters and their devices by observing the phones' attempts to join Wi-Fi networks. Daniel Cuthbert and Glenn Wilkinson created their own distributed data interception framework, dubbed Snoopy, that profiled mobiles, laptops and their users in real-time.

Smartphones tend to keep a record of Wi-Fi base stations their users have previously connected to, and often poll the airwaves to see if a friendly network is within reach. Although this is supposed to make joining wireless networks seamless for punters, it also makes it too easy for the researchers to link home addresses and other information to individually identifiable devices.

"We tested in numerous countries and during one rush-hour period in central London," Cuthbert told El Reg. "We saw over 77,000 devices and as a result, were able to map device IDs to the last 5 APs they connected to. Then using geo-location, we were able to map them out to physical locations."

"Apple devices were the noisiest based upon our observations," he added.

This phase of the project involved only passively listening to Wi-Fi network requests, rather than complete interception, making it legal under UK law. To help the pair process the huge volume of data collected, the researchers used a visualisation tool called Maltego Radium developed by third-party developers Paterva.

Cuthbert and Wilkinson set up Wi-Fi access points that collected probe requests of smartphones and other wireless devices before deploying a few of these around London, and using Maltego Radium to make sense of the data collected in real-time. "We could work out the most common movement patterns using the SSID probes sent out from their mobile phones," Cuthbert explained.

A similar system could be used by the unscrupulous to carry out targeted attacks.

"If we wanted to do illegal activities, we could pretend to be one of those networks, route all traffic through our central server and then perform analysis on the traffic," Cuthbert explained. "This would allow us to dump all credentials, strip down SSL connections, injecting malicious code into all web pages requested, grab social media credentials etc."

The research established that smartphones leak a lot more information than even tech-savvy people would imagine. "Apple, Google and so on do not have any documentation about how noisy their devices are," Cuthbert said.

The security bod advised users to use more common sense and disabling Wi-Fi scanning until they needed to actually access the web. "We will click on anything, and rarely turn bits off when outside, for example," Cuthbert explained. "People are more used to ensuring their laptops are secure."

The two researchers embarked on the six-month surveillance project as governments stepped up efforts to monitor of citizens’ internet-based communications - such as recording websites visited and emails sent - under the guise of countering terrorism.

Several private organisations, such as Palantir, have developed technologies to identify undesirable activities from collected data, or perhaps - according to the more paranoid - to profile all citizens.

Cuthbert and Wilkinson outlined the fruits of their research in a well-received presentation titled Terrorism, tracking, privacy and human interactions at the recent 44con conference in London. A first-hand account of this talk can be found here. A Naked Security podcast featuring an interview with the Sensepost team and banking insecurity expert Ross Anderson can be found here [MP3]. ®