When a complain was made against MS - the EU investigated and found:
Any abuse by one or more undertakings of a dominant position within the common market or in a substantial part of it shall be prohibited as incompatible with the common market insofar as it may affect trade between Member States.
Such abuse may, in particular, consist in:
(a) directly or indirectly imposing unfair purchase or selling prices or other unfair trading conditions;
(b) limiting production, markets or technical development to the prejudice of consumers;
(c) applying dissimilar conditions to equivalent transactions with other trading parties, thereby placing them at a competitive disadvantage;
(d) making the conclusion of contracts subject to acceptance by the other parties of supplementary obligations which, by their nature or according to commercial usage, have no connection with the subject of such contracts.
The evidence gathered during the investigation leads the Commission to believe that the tying of Internet Explorer with Windows, which makes Internet Explorer available on 90% of the world's PCs, distorts competition on the merits between competing web browsers insofar as it provides Internet Explorer with an artificial distribution advantage which other web browsers are unable to match. The Commission is concerned that through the tying, Microsoft shields Internet Explorer from head to head competition with other browsers which is detrimental to the pace of product innovation and to the quality of products which consumers ultimately obtain. In addition, the Commission is concerned that the ubiquity of Internet Explorer creates artificial incentives for content providers and software developers to design websites or software primarily for Internet Explorer which ultimately risks undermining competition and innovation in the provision of services to consumers.