Sure, most people (at least the ones who had already jailbroken their iOS4 devices) were mostly happy about the update that closed the security leak that would allow PDF files to transfer control of their devices to unruly hackers. But what about those with older Apple devices that aren't iOS 4 compatible? Well, it seems that the only answer may be jailbreaking.
Devices like the original iPhone, iPod Touch, and even iPhone 3G owners still running iOS 3.1.3 because the iOS 4 update ran too slowly on their phones did not receive the update that plugged the leak. Fortunately, searching for "PDF patch" on Cydia will give you a patch from Jay Freeman that will help you out. Of course, jailbreaking could possibly run you into other problems, so you may have to weigh the good and the bad. At least it's nice to see there's an option out there.