Apple today released iOS 4.3.4 (and iOS 4.2.9 for the Verizon version) with a fix for a recent PDF vulnerability. It also includes two other security fixes. Apple had acknowledged the PDF security issue earlier issue this week and promised a fix.
While there no reported attacks, the PDF vulnerability had been used by JailbreakMe.com to let user jailbreak their devices. Needless to say that the update will prevent you from using this latest jailbreak technique.
The latest iOS update is available for the iPhone 4, iPhone 3GS, iPad 2, iPad, and third- and fourth-generation iPod touch devices.