An iPhone developer has acknowledged that a recent update to one of his apps includes the hidden ability to tether the smartphone to a laptop, circumventing carrier fees for the service.

Chris Simpson, best known for creating apps for "jailbroken" iPhones, posted a walk-through on YouTube that shows users of his QuasiDisk app how to set it up for tethering.

By tethering a smartphone to a laptop, users can share the phone's cellular connection to the internet with a notebook. Carriers typically levy additional fees for the service.

Although QuasiDisk is billed as a "simple file manager and file viewer" that lets users load files, documents and photos from a third-party FTP server or sync data with a remote device using Apple's own iCloud, it also can be used for tethering, Simpson said in his instructional video.

The "What's New" section of QuasiDisk's App Store listing does not mention the functionality.

Simpson updated QuasiDisk to version 1.1 on January 28.

In the video, he spelled out the tethering process with QuasiDisk, which requires the user to start the app's FTP server, connect it to an "ad hoc" wireless network on a Mac or Windows notebook, and enter SOCKS and HTTP proxy settings on the laptop.

"That's tethering from the App store without paying your carrier," said Simpson near the end of the video.

Apple regularly - and quickly - boots tethering apps from the App Store, often with no explanation, but as of 8pm yesterday, QuasiDisk was still available on Apple's e-mart.

In November, Apple yanked an app called iTether within hours of its appearance on the App Store.

QuasiDisk currently sells for £1.49 on the App Store.

Apple did not immediately reply to a request for comment about QuasiDisk's tethering feature.

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