There are easily obtained tools that allow anyone to examine the API calls for executable programs and DLLs. The Windows API is fully published. There were some "secret" API calls in earlier versions of Microsoft Office but that ended some time ago as part of an earlier court order.

Given the number of alternatives, I still have a hard time understanding how Microsoft can have a monopoly on operating systems. My local electric company has a true monopoly - I have no choice about which company will sell me electricity. As for operating systems, in additions to Windows, I could buy an operating system from Apple (but only if I buy their hardware), Linux, Sun Solaris, Compaq Tru64 Unix, IBM's AIX, HPIX, AS/400, and probably several others that have slipped my mind at the moment. Several of those operating systems will run on my existing Intel hardware. The point is, anyone that wants to can get a computer system that doesn't use a single line of Microsoft code. Given all of these choices, how does Microsoft have a monopoly? Being dominant in the marketplace isn't a monopoly, and those of us who've worked in the computer industry for many years know how quickly marketplace dominance can be lost. Ever hear of Lotus 1-2-3 or WordPerfect?