Yes, he can exploit the Windows Update system and I can fly. :shy:
Microsoft said that Windows Update has the Microsoft root CA certificate hard-coded into it. If Windows Update finds out that the SSL certificate of update.microsoft.com is signed by any other CA (even legitimate ones like Thawte or others) other than Microsoft Internet Authority, it will fail. Plus, each of the Windows Update setup files are signed by Microsoft own certificate too, and if Windows Update encounters a update file signed by other legitimate CA that isn't Microsoft, the update will fail too.
The Comodohacker must have access to Microsoft private SSL keys (Microsoft Internet Authority) and also managed to hack into Microsoft servers to sign those Windows Update updates with the compromised certificate in order to deliver fake updates.