On the Support section of its website, Apple reveals that installing QuickTime 7.6.4 will disable the QuickTime Pro functionality in prior versions of QuickTime, such as QuickTime 6.
Recommended for all QuickTime 7 users, the new version also adds security fixes – three, to be precise, for Mac OS X v10.4.11, Mac OS X v10.5.8, Windows 7, Vista and XP SP3. QuickTime 7.6.4 includes changes that increase reliability, improve compatibility and enhance security, according to Apple.