> Thus, for Microsoft, "Windows" eventually acquired secondary meaning in the world of computer software (but not as applied to window installation in the building industry). Others can freely use "windows" in most any category of goods or services they want in the building trades but, given that the term "Windows" is now exclusively associated with a product from Microsoft in that class, not in the class of computer goods to which "Windows" belongs.

Note that they can't/don't sue products like wxWindows, even though it refers to windows on computer screens, because it refers to the generic usage and not in terms of a OS. Thus they sued Lindows (and lost?) because it was an OS and with a similarly sounding name and settled.