It turns out that it's actually a QuickTime flaw and more specifically a QuickTime Java flaw.. or so they seem to be saying now.
There's been a lot of confusion, with some blogs mixing in the two year old Mac Mini challenge and confusing that with this. That challenge involved giving the attacker a user account to work from; this one was done indirectly through a web page.
Of course some Windows folks are cheering wildly, but that's silly: most Mac fans are happy the bug was found and will be fixed. I wish they'd do this kind of thing more often: Apple, Microsoft, and everybody else with an interest in improving our Internet world should be ponying up prize money so that this kind of testing could be done every month. That could only improve life for everyone, right?