The iphones and iPads security is being called into question after it emerged the devices contain a hidden file that tracks the owner's locations.
The finding was reported by two British computer programmers at a technology conference in San Francisco.
The pair found Apple has been logging the whereabouts of 3G phone and iPad users since it updated its mobile operating system a year ago.
The location data is taken from mobile phone masts and Wi-Fi networks and recorded on the device along with the time and date.
However, one of the concerns is that when a person syncs their phone or iPad with a computer the information is transferred to the hard drive permanently.
Anyone with access to this computer, including a hacker, could then trace the user's movements.
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| Map showing a user's movements in south west England |
And if the phone or iPad was lost or stolen a stranger would also be able to view the data with the right software.
Although other mobile phone companies collect information in similar ways, it is usually kept behind a firewall.
It then normally requires a court order to gain access to it - but this is not the case with this data.
Pete Warden and Alasdair Allan, the researchers behind the discovery, have now set up a webpage to inform the public about the file.
On the page it states: "By passively logging your location without your permission, Apple have made it possible for anyone from a jealous spouse to a private investigator to get a detailed picture of your movements."
Mr Warden, who worked for Apple for five years, has created a free downloadable programme that allows them to see the location data on a map.
It is not known why Apple is collecting the data or whether the function can be disabled.
The criticism of the technology giant's operations comes after the company revealed on Wednesday that it had nearly doubled its second quarter profits.
