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Jay Freeman a.k.a saurik - founder and developer of Cydia has just released a new version Corona iOS 5.0.1 Untether jailbreak (v1.0-7) to fix the DRM iBooks issue.
iPhone Dev team had released a new version of Redsn0w - Redsn0w 0.9.10b5 yesterday that included a fix for the iBooks DRM issue. But the Corona iOS 5.0.1 Untether update that is available on Cydia is an easier option.
Saurik announced the availability of Corona iOS 5.0.1 on Twitter: