I disagree with the last two posters.
Open Source would result in hundreds of thousands of people who could check the code. Therefore it would be definitely more secure. In your own words, you say that "no one person can ever read or check" all the source code. Open source would be more secure because you have more eyes checking the code, and the more eyes you have on it, the more secure it is.
hundreds of thousands checking, maybe 10's of thousands adding code, then we go from 50 million lines to 75 or 100M?
If you are convinced open source is the solution go with one of the *nix based open platforms.
If you gain enough users then you become the target.
To say MS should give away, 5 years of 9500+ programmers/developers/managers time, which builds on 30 years of work, as an experiment in open source is silly, not only would MS management never consider it, stockholders would revolt.
The problems I see with open source are
take linux, people believe it is free.......it is not, much of the work (billions of $$$$$worth) has been donated by individuals, who at some point will hope to make money on it, or at least give less freely of their time. with that we have seen many proprietary efforts to commerialize it, most have failed, a few (mostly server versions) remain.
The lack of someone (a chief architech, so to speak) in charge, providing a consitant direction and goal for the 'product'.
Who has finally say as to what features are included/removed?
It may work on some projects, but businesses, will not consider it a viable 'product' (and thus provide a revenue stream=nessesary for long term survival) if the code can change daily at the whim of some fluid, ever changing group. (the cost of an in house IT staff checking and certifing each new addon for ANY O/S is a large part of the current "outsource mania")
Yes, Windows has become overly large and complex (like a deluxe swiss army knife, what good does having a fork on one end, and the blade on the other do when you want to cut your steak?) with too many other functions integrated in.