Windows Phone 8 security model
Despite all the rich features and customability of Android phones, they have some serious security issues - especially for those users who are less technical and don't know how to configure them for better security. The iPhone offers limited customability and doesn't have the features that many users want.
Microsoft is building Windows Phone 8 with multi-layered security defenses to protect against common exploits, to make it especially attractive to the enterprise.
Read more about that in the Microsoft Security Blog: