Expanding on allenbrunson's point, that's why it's correct to refer to them as a convicted monopolist. The word is indeed there precisely because "monopolist" does not carry the meaning of "convicted".... to be honest I'm not actually sure what your problem with the phrase is.
My problem with the phrase is unless I'm missing something, Microsoft was not found guilty of a crime (as sid_0 pointed out, U.S. vs Microsoft was a civil matter) and therefore the word "convicted" is meaningless. Actually, it could be considered slanderous.
This so far has been a community that prides itself on accuracy. If you're going to accuse someone of criminal acts, they should at least have been tried and found guilty in criminal court.
