Another anti-trust violation that was part of Microsoft’s suit was for product tying. Basically, it’s legal to obtain a monopoly in one product via competitive means, but it’s illegal for the company to then obtain monopolies with other products by tying them to the legal monopoly.

Microsoft was guilty of this vis-a-vis Windows, Office, and Internet Explorer (and maybe some server side stuff). Google may be guilty of it as well with Google Search, Chrome, YouTube, Gmail.