Apple granted Uber the unprecedented and "disturbing" ability to record what was displayed on users' iPhone screens, researchers have found.

Uber's app had special permissions that let it see what was happening on users' devices at any time, even while a different app was open according to Sudo Security Group. It could do this by accessing the colour data of every pixel on the display, meaning it could theoretically see what a user was doing.

If it had wanted to, Uber, or someone who had access to its system, could have used monitored customers' passwords and tracked their use of other taxi apps such as Lyft.

The iPhone maker gave Uber the extensive access, which could amount to an invasion of privacy if used to monitor devices, to improve how the Uber app worked with the Apple Watch.

"It looks like no other third-party developer has been able to get Apple to grant them a private sensitive entitlement of this nature," Will Strafach, chief executive of Sudo Security Group, told Gizmodo. "Considering Uber's past privacy issues I am very curious how they convinced Apple to allow this."