Apple has released a software update for its iPhone and iPad which prevents it keeping a detailed record of the owner's movements, and does not synchronise the details to the owner's computer.

The company had been criticised for the fact - discovered by two British researchers and revealed by the Guardian on 20 April - that the devices could effectively be used to trace where users had been, and that the file stored on the phone or tablet could be accessed by anyone who got hold of their computer. The data had been stored for up to a year.

Steve Jobs, Apple's chief executive, responded to a concerned user on 25 April that "we don't track anyone". It also emerged that Android phones keep a similar cache of data, though only if the user gives permission. Apple users give similar permission, though it is buried in the 15,000-word agreement to use the iTunes store.

Apple said in a statement on 27 April that the file was in fact a record of mobile cell towers and Wi-Fi networks that the phone had "seen" in order to help it calculate its location more rapidly and accurately than if it were using the GPS satellite location system. Some of the towers, it said, could be up to a hundred miles away from the iPhone or iPad that recorded them.

The update cuts the amount of cached data that is stored to just a week, and does not synchronise it to the owner's computer if the phone or tablet is connected to it. That means that if someone gets at the computer they will find no details. In addition, the cached data is wiped if the user disables the location services setting on the iPhone or iPad.

The data is not encrypted on the device, which means that it could be collected by law enforcement or thieves. But Apple says it will encrypt the data in another forthcoming update to the software that runs the devices.

On 27 April, Apple said "users are confused, partly because the creators of this new technology (including Apple) have not provided enough education about these issues [of data storage for determining location] to date."

The update applies to the iPhone 4, iPhone 3GS, iPad 2, iPad, and the 3rd and 4th iterations of the iPod Touch. However the iPhone 3G will not receive the update. Apple has not said what will happen for those users.