Late on Wednesday, Apple posted QuickTime 7.4.1 which addresses security issues and improves compatibility with third-party applications.
Background information and applicability is provided on the Apple Security Updates page. The release applies to both PPC and Intel Macs as well as Windows Vista and Windows XP. Mac OS X updates are available for Leopard, Tiger and Panther.
Apple didnit cite which third party applications were affected, but that part might have something to do with previous reports regarding problems with Quicktime 7.4 and Adobe After Effects.
The update has also appeared in System Preferences -> Software Update for PPC and Intel Macs.