Apple have released QuickTime 7.6.4 that contains security updates. Apple state that this release is recommended for all QuickTime 7 users.

This version can be downloaded and installed via Software Update preferences, or from Apple Downloads.

QuickTime for Windows can be downloaded from Apple downloads at

http://www.apple.com/quicktime/download/

select the option with or without iTunes as appropriate.

For full details on the security content of this update see this Apple document:

http://support.apple.com/kb/HT3859