The European Union's executive arm formally accused Microsoft of failing to comply with a binding agreement to give customers a choice among Internet browsers.
In 2009, the European Commission accused Microsoft of using its dominant market position to foist its Internet Explorer browser on users. In negotiations, Microsoft agreed to create a screen where users could choose among competitors' browsers. The Commission accepted that concession and made the creation of a "browser choice screen" legally binding.
But in July, the Commission said the screen had not been displayed on many computers between February 2009 and July 2012 and millions of users may have been affected during that period. At the time, Microsoft said that a technical error was responsible.
The company retained outside counsel to conduct a formal investigation into how the error occurred and to make suggestions to avoid such problems in the future.
The Commission's investigation into the possible antitrust breach has continued, and today it formalised its complaint. The next step is for Microsoft to respond to the complaint; then the Commission will make its decision.
Microsoft could face a fine of up to 10 percent of its annual revenue if found in breach of antitrust law.