I’m totally not surprised that Apple has managed to fix that PDF security flaw, which is believed to have been used by the iPhone Dev Team to jailbreak the iPhone 4, and all the other iOS 4 devices with JailbreakMe 2.0.
Cupertino has probably been working around the clock to address the PDF security hole that is believed to have been exploited by the iPhone Dev Team, but that could also be used by other hackers to attack iOS 4 users. The next major iOS update will probably come with this fix onboard, and once installed it will break the JailbreakMe jailbreak process. In case you don’t want to do that then you simply have to stay away from future Apple iOS upgrades at least until the iPhone Dev Team jailbreaks the next iOS version too.
It will be interesting to see what the iPhone Dev Team will do now when it comes to iPhone 4 jailbreaking and unlocking, but, just as we’ve seen in the previous years, almost every iOS version has been successfully jailbroken so far.