London - Officials demanded on Monday that an advertising firm stop using a network of high-tech trash cans to track people walking through London's financial district.The Renew ad firm has been using technology embedded in the hulking receptacles to measure the Wi-Fi signals emitted by smartphones, and suggested that it would apply the concept of "cookies" - tracking files that follow internet users across the Web - to the physical world."We will cookie the street," Renew Chief Executive Kaveh Memari said in June.But the City of London Corporation insisted that Renew pull the plug on the programme, which captures smartphones' serial numbers and analyses signal strength to follow people up and down the street. Renew didn't immediately return a call seeking comment on whether it would comply with the authorities' demand.The trash cans join a host of everyday objects from televisions to toilets that are being manufactured with the ability to send and receive data, opening up new potential for interaction - and surveillance.It's unclear how Renew had planned to use the data, which was gathered by its reinforced, shoulder-height pods stationed near St Paul's Cathedral and Liverpool Street Station.But if a company could see that a certain smartphone user spent 20 minutes in a McDonald's every day, it could approach Burger King about airing an ad on the bin's video display whenever that user walks by at lunchtime. Or it could target its commercials in real time by distinguishing between people who work in the area and visiting tourists.The prospect drew comparisons to the creepy "Good evening, John Anderton" ads from the Tom Cruise thriller Minority Report.Spy binsRenew first tested the technology using 12 trash cans in May, but the story didn't get traction until last week when a sudden burst of publicity surrounding the "spy bins" put authorities on the defensive."Anything that happens like this on the streets needs to be done carefully, with the backing of an informed public," read a statement from the City of London Corporation, which is responsible for the city's historic "square mile," home to financial institutions, law firms and tourist landmarks.A spokesperson for the body said it had been blindsided by the tests, which he said it learned about through the press only last week.Britain's data protection watchdog said it would investigate, while Nick Pickles of the privacy advocacy group Big Brother Watch said questions need to be asked "about how such a blatant attack on people's privacy was able to occur."In a recent statement, Memari said media coverage of the "spy bins" had been a bit breathless."A lot of what had been extrapolated is capabilities that could be developed and none of which are workable right now," he said.