Read this: "CyberInsecurity: The Cost of Monopoly" [PDF, 878KB, 24p.], it is good. From the executive summary:
The threats to international security posed by Windows are significant, and must be addressed quickly. We discuss here in turn the problem in principle, Microsoft and its actions in relation to those principles, and the social and economic implications for risk management and policy.
In fact one of the six authors of the above paper, Dan Geer, was fired (See the Boston Herald and eWeek articles) from his job as CTO for @stake, a supplier for Microsoft among others, because of it, the day before the paper was publicised by CCIA.