SAN FRANCISCO -- Apple Inc's iPhone is collecting and storing user's location data even when location services are turned off, the Wall Street Journal reported on Sunday after analyzing data and documents.

According to a test conducted by the newspaper, the location data appear to be collected using cellphone towers and Wi-Fi access points near a user's phone and don't appear to be transmitted back to Apple, said the report.

It noted that the new finding is likely to renew questions about how well users are informed about the data being gathered by their cellphones.

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On Friday, the Wall Street Journal reported its security analysts had found that Apple's iPhone and smartphones running Google's Android operating system regularly transmit users' locations back to the two companies respectively, which is part of their race to build databases capable of pinpointing people's locations via smartphones.

Worries on the iPhone tracking issue surfaced on Wednesday after two British researchers announced at a technology conference in California that iPhone has been collecting users' location information and storing the data for extended periods of time.

The researchers said starting on June 21, 2010, after the release of iOS 4 mobile operating system, iPhones began logging and storing location information in a file, which shows the users' latitude and longitude and is timestamped to the second. They noted the information is not encrypted on the phone or on the iPhone backups made by iTunes and the file is also persistent, transferring itself to a new iOS device when the old one is replaced.

They added they had no evidence that the file was being transmitted to Apple.

On Thursday, US congressman Edward Markey reacted angrily to the news in a letter to Apple CEO Steve Jobs, asking Jobs to make a response within 15 business days or no later than May 12.

On Saturday, Markey called for a congressional investigation into the privacy practices of Apple and Google. In a statement, he made clear that he thinks the data collection is potentially dangerous, saying predators could have hacked into an iPhone or Android to find out children' s location information.