QuickTime 7.7.6 improves security and is recommended for all QuickTime 7 users on Windows. For information on the security content of this update, please visit this website: http://support.apple.com/kb/HT1222.
Important Notice to QuickTime 6 Pro Users
Installing QuickTime 7 or later will disable the QuickTime Pro functionality in prior versions of QuickTime, such as QuickTime 6. If you are a QuickTime 6 Pro user and you proceed with this installation, you will need to purchase a QuickTime 7 Pro registration code in order to regain QuickTime Pro functionality. After installation, visit the Apple Online Store to purchase a QuickTime 7 Pro registration code.
See this article for details on how to verify the authenticity of this download.