The udpate is available for the GSM iPhone 4, but no update has been made for the CDMA iPhone 4. That device is still on iOS version 4.2.6, released in January.
The iOS 4.3.1 update is also available for the iPhone 3GS, iPad 2, iPad and the third- and fourth-generation iPod touch. According to Apple, the update includes:
Fixes an occasional graphics glitch on iPod touch (4th generation)
Resolves bugs related to activating and connecting to some cellular networks
Fixes image flicker when using Apple Digital AV Adapter with some TVs
Resolves an issue authenticating with some enterprise web services
This week, it was rumored that Apple would issue iOS 4.3.1 within two weeks, making Friday's release somewhat unexpected. The accompanying notes make no mention of battery issues reported by some users of iOS 4.3, nor does it say whether a security hole exposed at a recent hacker conference has been patched.
News of iOS 4.3.1 came earlier this month via the Pwn2Own hacking contest, when security researcher Charlie Miller revealed that Apple has a fix in the works for a flaw in its Safari mobile Web browser. Miller exposed the flaw at the contest, and privately shared the exploit with Apple to help the company patch its software.
Also Friday, Apple released Xcode 4.0.1, also a minor update. Changes to the software, according to Apple, include:
Improved Assistant editor logic when switching among different file types
Fixed a bug in "Install Xcode.app" that hangs at 99% complete, never finishing
Fixed a bug that prevented indexing of some projects
Fixed a bug related to nil settings in the Core Data model editor
Fixed a bug that prevented automatic download of iOS documentation
Fixed a bug in LLVM GCC 4.2 and LLVM compiler 2.0 for iOS projects
Additional bug fixes and stability improvements