It says reports last week that they could be used to track their owners' whereabouts was a misunderstanding of how the phones help determine where they are.

The company said the data file uncovered by researchers and publicised is not a log of a phone's location, but a list of Wi-Fi hotspots and cell towers nearby. That helps the phone work out its location without having to listen for faint signals from GPS satellites.

Apple also said a software bug caused the phones to keep the data longer than intended.

It is the first comprehensive response to claims that iPhones store up to a year's worth of user location data.