From Apple's website:
"A heap buffer overflow exists in QuickTime's handling of HTTP responses when RTSP tunneling is enabled. By enticing a user to visit a maliciously crafted webpage, an attacker may cause an unexpected application termination or arbitrary code execution. This update addresses the issue through improved bounds checking."
It's about ~50 Mb. I suggest you go ahead and update. (This is in addition to the iLife and iWeb updates from this week. Go ahead Apple, update away)
Subscribe in a reader