Apple has released iOS 4.3.4 for iPhone, iPad and iPod Touch devices. This update is said to have security fixes but it is important to note that it also fixes the PDF exploit in mobile Safari.
Because the JailbreakMe 3.0 iOS Jailbreak relied on this exploit it is now blocked. So anyone relying on this Jailbreak is advised to avoid getting this update. For more information on Jailbreaking click here.