The US Congress is to hold a hearing about mobile phones and privacy after claims that Apple devices have been secretly tracking users' location data.
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Researchers Alasdair Allan and Pete Warden have claimed that Apple iPhones and 3G iPads record users' location data.
These records are stored in an unencrypted format and can be accessed by anyone who gets hold of the equipment, they told the O'Reilly Radar blog.
News of the investigation, which is scheduled for 10 May, comes after Apple's refusal to comment on the researchers' claims or respond officially to queries from members of the US Congress, according to US reports.
South Korean and European data protection authorities have also announced similar investigations.
Several private individuals in the US are said to have begun filing lawsuits alleging Apple has invaded their privacy.
The investigation by Congress follows reports that other researchers have discovered that phones based on Google's Android operating system also track user location.
Google, which has been invited to the hearing by Congress along with Apple, has issued a statement saying that their phones do not track users unless they opt in.
Google also claims that any location data that is sent back to the company's location servers is anonymised and cannot be linked to a specific user.
Apple and Google have both previously said that users can turn location data off by disabling location services.
But, according to the Wall Street Journal, turning off location services does not disable the storage of location data on iPhones.
In independently verified tests, the paper found that an iPhone 4 restored to factory settings with location services disabled still recorded location data.
This data included coordinates and time stamps, but the coordinates were not exact and did not indicate how much time was spent in a given location.