The functionality was introduced in June as part of a mobile device management (MDM) bundle for iOS 4.0, intended to be used by enterprise applications for businesses. Once an iPhone declared itself jailbroken via Apple's API, an enterprise application could take actions to prevent the possibly unsecure device from connecting to a corporate network or e-mail server. In version 4.2, however, the API has been removed, leaving vendors perplexed as to why. Third-party MDM vendors had created their own utilities to check for jailbreaks, but Apple's jailbreak detection API allowed MDM applications direct access to iOS system information.
Jailbreaking allows users to install applications that haven't gone through Apple's App Store screening process and that potentially can take advantage of APIs typically reserved for built-in iOS applications. The process has been a major concern for Apple since users do so to pirate App Store software or to use their device on other carriers. Although doing so voids Apple's warranty, the US government recently legalized jailbreaking. Nevertheless, Cupertino has found itself in a kind of cat-and-mouse game with hackers: as soon as the company implements a new method for protecting its phones, someone always finds a way to work around the new code.