Confirmed on Windows XP, Windows Vista and Windows 7:
A security researcher has unearthed a “bizarre” flaw in Apple's QuickTime Player that can be exploited to remotely execute malicious code on Windows-based PCs, even those running the most recent versions of operating system.
Technically, the inclusion of an unused parameter known as “_Marshaled_pUnk” is a backdoor because it is the work of an Apple developer who added it to to the QuickTime code base and then, most likely, forgot to remove it when it was no longer needed. It sat largely undetected for at least nine years until Ruben Santamarta of Spain-based security firm Wintercore discovered it and realized it could be exploited to take full control of machines running Windows 7, Microsoft's most secure operating system to date.
More at Apple QuickTime backdoor creates code-execution peril • The Register