EU hits Microsoft with $731 million antitrust fine

But according to the European Commission, Microsoft failed to display the browser choice screen with its Windows 7 Services Pack 1. The commission said that as a result, 15 million European Windows users did not see the choice screen from May 2011 until July 2012.

"Legally binding commitments reached in antitrust decisions play a very important role in our enforcement policy because they allow for rapid solutions to competition problems. Of course, such decisions require strict compliance," Joaquín Almunia, Europe's top antitrust regulator, said in a statement. "A failure to comply is a very serious infringement that must be sanctioned accordingly."

It is the first time that the commission has fined a company for non-compliance with a decision. The commission said it took into account the "gravity and duration" of the infringement, the desire to ensure a deterrent effect and, as a mitigating circumstance, the fact that Microsoft cooperated with the investigation. 

Microsoft has blamed the failure to display the screen on a technical glitch and has said it has since strengthened internal procedures.

"We take full responsibility for the technical error that caused this problem and have apologized for it," the company said in a statement. "We provided the Commission with a complete and candid assessment of the situation, and we have taken steps to strengthen our software development and other processes to help avoid this mistake – or anything similar – in the future."

—Updated at 10:00 a.m.