Info om foreksempel en av jailbreakene jeg vet om, JailbreakMe 2.0:
Firstly, don't update past 4.0.1, the last firmware JailbreakMe supports. Secondly, and arguably most importantly, allow Cydia to "make your life easier". This will allow you to always restore back to the latest firmware available when you select that option.
Altså, SHSH blobs.