Dear fellows:
We need to put things in perspective, calm and easy. I could just say that the statement from Microsoft's CEO is false, but I'll not. Instead I'll will just describe some facts and then you reach your own conclusions.
The main problem with security on windows and other operating system is in their base. Unix like OSs are closed systems by default while Microsoft Windows is a open system by default. On Unix like OSs in order for a user to run anything you need first to give him necessary permissions to do so. Otherwise not even a byte the user can read from whereever. On Windows you can do what so ever and then you starting removing power to a user (closing the system to that user).
When a trojan or a virus infect an OS it operates under a user account, so it inherits the system previleges of the user under who's account it is running and only that user. On Windows OSs because the users by default are at least machine administrators the virus or trojan is able to do whatever that user can, so it damages the system alot more than on Unix like OSs.
Try as a normal user on Unix based systems to access the configuration files. Yes in many of them you are even able to read those files, but you can't change a thing on them. Try to delete a file in the /USR (kind of Program Files under windows) directory for example, you can't.
Try to map a network drive or even access to your CD-ROM it will tell you that only the system administrator can do that and because on Unix nobody works as system administrator then the system core never has a virus. In the worst case scenario only the files created by the user can be deleted or damaged not the files from other users so even if we had virus on Unix the impact over the system would be very small (to the user level only). On Unix, as soon a user logs out from the system all applications running with that user permissions are forcelly terminated by the OS itself. Because the Unix system administrator (ROOT) only logs in for bref moments (the way it should be used) root has no internet mail, only local mail, root has no need to browsers (you do it under or normal user account) and so on. On windows virtually any user can delete, create or modify any files, becuase by default your user is the system administrator.
Now just think a little Best regards Joao Ribeiro da Silva