The iPhone Dev Team has already jailbroken Apple's new iOS 4.3.4 release, pushed out to the iPhone, iPad and other devices on Friday last week. The updated iOS version patched a PDF vulnerability which hackers had used to jailbreak iOS 4.3.3; however, redsn0w 0.9.8b3 has been released to handle jailbreaks on 4.3.4, albeit tethered rather than untethered.
For the uninitiated, a tethered jailbreak means that should you need to power-cycle your iPhone or other iOS device, you'll need to have it plugged in via USB to your computer else you will lose the hack. An untethered jailbreak is preferable, because it removes that limitation.
The message from the iPhone Dev Team is that most users should stay on iOS 4.3.3 and not update at all; there's no new functionality to be had, only the security fix (which can be achieved with a third-party app called PDF Patcher 2, available from the Cydia unofficial app store). Meanwhile this new jailbreak won't work on the iPad 2, and is being billed as primarily for the benefit of kernel hackers who want to work on the very latest firmware version.
Nonetheless, the road ahead for iOS jailbreakers looks to be trickier than ever. iOS 4.3.4 reportedly also closed off too other loopholes hackers had been using for untethered solutions - an integer overflow-related bug and an incomplete code signing issue. Meanwhile, iOS 5 will reportedly block firmware downgrades using a new signing system.