This isn't the larger iOS 5.1 update that's currently in the hands of developers, but Apple has seemingly re-released 5.0.1 today with a new build — 9A406 instead of the earlier 9A405 — that's only available for the iPhone 4S, specifically. Well-known iOS hacker MuscleNerd recently tweeted an unusual observation about the update: it's the first official 4S firmware with an accessible encryption key for the main file system, meaning you can browse the file system from a PC unimpeded. Lots of folks are pointing out that this means users will be able to get at Siri's files without committing piracy, and that could lead to a field day for Siri hacks. There's no official word from Apple at this point on exactly what's changed.