It was a holiday gift ten years and billions of dollars in the making. On December 16, 2009, Microsoft Corporation’s legal department settled the company’s longest and most expensive antitrust legal battle. In a major concession to European regulators, the software giant agreed to open its Windows operating system to rival Web browsers.

Microsoft’s general counsel, Brad Smith, and his legal team spent months last year hammering out the details of the 61-page settlement with the European Commission, the European Union’s executive body. By fall, Microsoft’s legal department had held 24 videoconferences and 34 conference calls with E.C. lawyers. “We wanted to be seen as a company that would work with regulators,” says deputy general counsel David Heiner, who heads the antitrust group and led much of the negotiations.