Apple has updated its QuickTime software, now at version 7.6.9, to fix vulnerabilities where a maliciously designed file could execute arbitrary code or lead to the application terminating.
As Apple describes in its knowledge base article:
"Description: A heap buffer overflow exists in QuickTime's handling of JP2 images. Viewing a maliciously crafted JP2 image may lead to an unexpected application termination or arbitrary code execution. This issue is addressed through improved bounds checking. For Mac OS X v10.6 systems, this issue is addressed in Mac OS X v10.6.5. Credit to Nils of MWR InfoSecurity, and Will Dormann of the CERT/CC, for reporting this issue."
Also included in this security update are fixes to maliciously crafted AVI file types, other movie file types, FlashPix image files, GIF image files, or PICT image files, as well as a possibility that local users may have access to sensitive information on certain Windows machines.