The iOS app iRandomizer Numbers contains an unexpected function: It allows users who enter the undocumented codes to create a tethered Internet connection. Thereafter, other nearby computers can join an ad-hoc WiFi network and reach the Internet using the tethered iPhone's cellular data connection.

The app purports to be nothing more than a random number generation tool. But entering "1984" in the minimum field and "31337" in the maximum field--numbers of significance in the hacker community--and tapping the "generate" button reveals a tethering network configuration screen.

The inclusion of hidden or undocumented features in an iOS app is forbidden under Apple's App Store Review Guidelines.

Tethering is easier on Android phones, through apps like ClockworkMod. Both AT&T and Verizon have tried to prevent Android phones from using tethering apps.

Nick Kramer, CEO of Shmoopi, LLC, acknowledged in an email that his app supports tethering. "Reluctantly, I will admit that my application 'iRandomizer Numbers' does have a hidden tethering feature," he wrote. "I say reluctantly because I didn't plan on the feature being released. I designed the tethering functionality for my family and close friends not thinking it would be disseminated outside that circle. "

[ The NSA is working on a plan to make commercial mobile devices secure enough for the agency to use. Read National Security Agency Plans Smartphone Adoption. ]

In a phone conversation, Kramer said he was aware that Apple had removed at least three other apps that supported tethering from its App Store. Handy Light, removed in 2010, was one such app.

He said that he was aware of a few other apps like this that have not been released.

Kramer suggested the $4.99 price tag--high for an app with so little apparent functionality--was intended to limit its distribution. Shmoopi, LLC, offers several other apps, which collectively have racked up over 300,000 downloads.

Kramer said he has no immediate plan to withdraw the app now that news of the feature has made it to online discussion boards. "The most I've seen happen to developers is that Apple takes their app down," he said. "But I'm afraid if I leave it, they could make an example of me."

Apple did not immediately respond to a request for comment.

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