Ok then they post an update it might be IE. So I guess noone knows, or it depends on the contracts you have with Adobe.

From an earlier /. article: http://arstechnica.com/security/news/2010/01/researchers-identify-command-servers-behind-google-attack.ars

From the article in this post: The previously unknown flaw in the IE browser was probably just one of the vectors used in the attacks .
I love the "probably"

Yes everyone has flash, but what they don't tell you is that you'll also need the Swarmcast NexDef browser plug-in.
Check out the not so great review of the flash/nexdef experience: MLB Support Forums

Oh and if you want to also understand this from Microsoft's perspective: Miscosoft SL Team Blog
The CBS March Madness HQ streaming was SilverLight and was a huge success.