I'm not a strident pro-MSer either - otherwise I wouldn't have an Android phone and tablet. But I also know that not all Open Source software is honest - they have gotten caught more than once pirating code from commercial products into their own.
Not from the big players. Microsoft guards its code like Fort Knox. It has released select pieces of code to its OEM developers only under very strict NDA but never enough to put anything significant together, not counting the leaked Win2K source code, which really bore nothing of interest to the Linux community. It did provide some very funny and embarrassing remarks from developers throughout the code, though.
Not all open source projects are innocent. Linux, however, has been quite vigilant at keeping anything copyrighted out of their code. Patents, however, are a little more difficult. The problem with patents on software and algorithms is that they can be too broad and vague. The patents may describe a process without actually having any code, leaving it open to loose enough interpretation to cover just about anything resembling its process.
Patents that should not be allowed include software, algorithms, equations, color schemes, fonts and pretty much anything that is abstract and intangible. Patents were conceived to protect inventors, not hunches or methods. Abstract ideas are not inventions. You may copyright your version of its implementation but to feel like one has some inherent right to suppress its implementation in any other form is purely arrogant and its intent is to stifle innovation or any improvement upon its concept, nothing less.
In the seedy world of patent trolling the worst offender by far is Apple. This is in part because they managed to exploit a brain dead patent office to get things patented that never should have been (a rectangle with rounded corners...really??) and their constant attempts to get competitor devices banned from the market. This is why I am roundly on Samsung's side in their Apple case - and the more that comes out about the jury and especially the foreman the more I expect it will be reversed on appeal.
The whole rounded corner argument is epically ridiculous. Any jury not seeing that as trivial at worst, blatantly obvious at best, is brain dead.
Both Microsoft and Apple have heavily exploited the patent office's ineptness at sniffing out triviality. Apple has been more public and vocal about its patent whoring whereas Microsoft is quietly going after the OEMs instead of facing Google head-on. Both these entities are a thread to innovation.