Why you are identifiable after just a few steps

Airport security may soon have a new way to check your ID: watching the way you walk. It seems footsteps are as unique as fingerprints, and can identify people with 99.8 per cent accuracy.

"For the first time, our results show that it probably is possible to use this in a real-world security application," says Todd Pataky of Shinshu University in Nagano, Japan.

Earlier studies suggested that everyone walks in a unique way that can be captured on film or by pressure sensors. But these studies tended to look at only 10 people each, making it difficult to tell how well the methods would work in the real world.

So Pataky and colleagues asked 104 people to walk across a half-metre-long board studded with thousands of pressure sensors, recording ten steps per person. The sensors recorded how each foot applied pressure to the ground, and how that pressure distribution changed as the person walked.

Patterned footsteps

The information collected was then input into a computer and used to train an algorithm to pick out the patterns in people's steps. Of the 1040 steps recorded, the algorithm wrongly identified only three – a 99.8 per cent success rate.

"Even if they have the same foot size, even if they have the same shape, [people] load their feet differently, and they do it consistently," Pataky says. Similar sensors, which are available commercially for about $20,000, could be used in airports to identify passengers as they walk barefoot through security.

Christopher Nester of the University of Salford in the UK thinks the technique could be used as a diagnostic tool for foot diseases and orthotics. As for security applications, he sees another, perhaps overlooked, drawback. "Nobody minds putting their fingertip on a glass surface, which is clean," he says. "But we very rarely wash our feet."

Twitter board loses two power players

SAN FRANCISCO (CNNMoney) -- Three behind-the-scenes power players have left Twitter, the latest in a series of departures that are reshaping the micro-messaging site.

Board members Fred Wilson and Bijan Sabet, two of Twitter's earliest investors, are stepping down, the company said Friday. On Thursday, Twitter Chief Scientist Abdur Chowdhury confirmed that he is leaving the company.

"Bijan Sabet and Fred Wilson both played important and greatly appreciated roles in our success," Twitter said in a written statement. "Both saw what Twitter could become before most anyone else. We look forward to their continued input as both investors in the company and passionate users of the product."

Twitter recently completed a massive $800 million funding round, half of which went to cash out part of the holdings of some early investors, including Wilson's firm, Union Square Ventures. USV kept some of its stake in Twitter.

Twitter's $400 million war chest will help the five-year-old company tackle a problem of growing urgency: Building a sustainable business on top of its widely used, free platform. In a "State of the Union" talk last week, CEO Dick Costolo publicized the latest Twitter stats: 100 million active users log in at least once a month.

Costolo took over in October as the company's CEO, assuming the reins from co-founder Evan Williams, who planned to step back and focus on product development. But just a few months later, Williams ceded that role to once-exiled co-founder Jack Dorsey, who now juggles his Twitter duties with his CEO role at payments venture Square.

Williams and Twitter's third co-founder, Biz Stone, have faded away from active involvement at Twitter. In June, they launched a new venture: Obvious Corp., an incubator for companies focused on "building systems that help people work together to improve their lives and the world."