US-Cert advises all users of Apple Quicktime to install a new version (7.1) which addresses mutliple vulnerabilites; these vulnerabilites might permit a remote attacker to execute arbitrary code or cause a denial-of-service condition if a user could be convinced "to access a specially crafted image or media file using a vulnerable version of QuickTime."
http://www.us-cert.gov/cas/techalerts/TA06-132B.html
The stand-alone Quicktime Player 7.1 for Windows or Mac OSX can be downloaded here:
http://www.apple.com/quicktime/download/standalone.html
Regards,
John