Businesses which rely on Microsoft security issues (Score 1)

There is an entire industry based on fixing Microsoft security flaws. Norton, Symantec, etc... all do a significant portion of their business working around Microsoft flaws. There are billions of dollars to be made off of Microsoft flaws, so much so that Microsoft recently decided they wanted a piece of the pie by purchasing anti-malware products. What incentive does Microsoft have for fixing flaws that support an entire industry, especially one which Microsoft itself profits from?