Geohot, a well known iOS hacker who left the scene last year, has magically re-appeared, bringing Limera1n, which will jailbreak all iOS 4.1 devices. Right now it’s Windows only, and buggy as all getout, but it sounds like those are all being fixed.
Since this is a completely new exploit, the team behind the hotly anticipated GreenPois0n have decided to delay releasing their app, as there’s no point in both putting out different tools, and having two exploits exposed and patched by Apple at once. GreenPois0n will wait until the next iOS upgrade:
The release of limera1n has (hopefully!) averted the burning of 2 bootrom holes at once (both his and SHAtter). Releasing SHAtter now would be a complete waste of a perfectly good bootrom hole in light of limera1n, and so it can be held until Apple closes limera1n’s hole. While there’s no guarantee that Apple won’t also close SHAtter by then, it provides a ray of hope for devices after Apple’s bootrom respin. Meanwhile, look for an alternate implementation of the limera1n exploit in greenpois0n (and possibly other tools), where it should undergo more testing too.
They also say not to use Limera1n if you used the Ultrasn0w carrier unlock, instead wait for PwnageTool to incorporate Limera1n in order to not lose your unlock.
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Or use TinyUmbrella to upgrade to 4.1 without upgrading the baseband.