Changes
QuickTime 7.6.6 classid
With each QuickTime release, the classID for the registry check and uninstall command changes. To find the correct classID for unknown QuickTime versions, try running <code>strings QuickTimeInstaller.exe | egrep '\{[0-F]+(-[0-F]+){4}\}'</code>.
For example, QuickTime 7.6.5 6 uses <code>{8B7917E028BE306E-AF555DA6-4E8A4F9C-9473BDB0-017F0AA03AC8DBA3C8C6FFFD}</code>.
Now you only have to delete the Registry key "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" -> "QuickTime Task".