The World: New York - Facebook purchase tracking angers members

Facebook has provoked a row with thousands of users who complain that its new marketing programme is publicising their purchases for friends to see.

The initiative was unveiled by the Facebook chief executive, Mark Zuckerberg, two weeks ago. Users have complained that they did not notice a small box on a corner of their web browsers following transactions with Fandango, Overstock and other online retailers.

The box alerts users that information is about to be shared with Facebook unless they click on "No thanks". It disappears after about 20 seconds, after which consent is assumed.

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