Apple has just released the latest update for iOS 4.0.x (iPhone, iPod touch) and iOS 3.2.x (iPad). Previous versions of the mobile operating systems had a PDF vulnerability that was exploited by the iPhone Dev Team to jailbreak the devices.
The iPhone Dev Team was able to make an incredibly simple jailbreak (for the end user) that simply required users to visit the website JailbreakMe.com to jailbreak their devices. The jailbreak was followed up by a software unlock which allowed the iPhone 4 to be used on other GSM networks (in the case of U.S. customers, T-Mobile).
With this security update, that loophole is obviously closed, so the ball is back in the iPhone Dev Team’s court to find another iOS security hole to expose.