Scanlife, a provider of QR code services, saw the number of unique users scanning codes through its system triple in the year to March.

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The 33 million figure Pincus quoted may then have been the number of unique, rather than repeat, users.

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At stake is--pick a number--billions of potential users and ever-more unique ways to separate cash from Web users.

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Since the last seven digits of a phone number are not unique and are in the public domain, the security of the system would be undermined if two users' fingerprints were similar enough to generate a false acceptance.

ECONOMIST: Security