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(PA)

Apple iPhones and iPads are making it possible for jealous spouses and private detectives to track their users' every move, researchers claim, after discovering the gadgets secretly track their owners' whereabouts, storing the information in unencrypted files.

Apple is coming under increasing pressure to explain to angry customers why its products have been storing the location data after it refused to be drawn on yesterday's reports. Campaign group Privacy International accused the company of "astounding arrogance" over its "continued refusal to take part in any dialogue over privacy".

It emerged Apple's products had been collecting the data after research by two British security experts came to light. Privacy International last night wrote an open letter to Apple, saying its phones had been "ringing off the hook with Apple users feeling betrayed and deceived". It said it wanted to know why the file was created; who, exactly, has access to it; how Apple can ensure it is not accessed by unwelcome intruders; whether the company will allow users to opt-out; and whether it will release a statement to its customers, explaining its policies on privacy.

"Apple thinks it knows better than the rest of the industry when it comes to privacy. Other companies have faced heavy sanctions recently and now the finger is being pointed at Apple. They cannot continually refuse to engage," said Eric King of Privacy International.

It emerged yesterday that later versions of the iPhone, as well as other 3G-enabled Apple devices, collect location data and timings automatically, saving them in a file on both the handset and on the computer used to manage the device. The file is also transferred to new devices after they are plugged into that computer. After installing a simple programme, versions of which are available online, anyone with access to the hardware can see a detailed map of the owner's movements. It is unclear whether the feature can be disabled.

"In the wrong hands, that sort of information can be very dangerous," said Mr King. "There are a lot of things someone could easily deduce given that level of information."

Apple refused to explain why the devices, believed to have been first included in June 2010, had been designed to store the information. Security experts Pete Warden and Alasdair Allan do not believe the information is transmitted to Apple itself.

Mr Warden, a British researcher who used to work for Apple, said the company "has made it possible for almost anybody – a jealous spouse, a private detective – with access to your phone or computer to get detailed information about where you've been".