The Commission has been investigating Microsoft since 1998, when competitors accused the company of failing to disclose hardware specifications necessary to integrate non-Microsoft software into corporate networks.
The long-running investigation began drawing to a close in August this year, when the Commission issued a preliminary finding that Microsoft's practices in Europe were anti-competitive, but gave the company a final chance to put its case.
The company has given a written response to the Commission and has spent one and a half days giving oral and videotaped presentations in a closed-door hearing that began on Wednesday.
The bulk of the argument given by Microsoft has focused on allegations that Microsoft is leveraging its dominant position from the PC into low-end servers and that Microsoft's tying of Windows Media Player to the Windows PC operating system is anti-competitive.
The Commission has already indicated that it is prepared to order that Microsoft reveal the necessary source code to allow rivals such as Sun Microsystems to achieve full interoperability with Windows PCs and servers, and thus – in theory at least – compete on a level playing field.
With respect to tying, the Commission has set out two alternative proposed remedies. The first would be the untying of Windows Media Player from Windows, whereby Microsoft would be required to offer a version of Windows without Windows Media Player included. This is a normal remedy for a tying infringement.
The second would be a "must-carry" provision, whereby Microsoft would be obliged to offer competing media players with Windows. Both solutions seek to ensure that consumers have a fair choice of media players.
The Commission also has the power to fine Microsoft up to 10% of its global turnover – a turnover that amounts to around $30 billion.
In a statement to reporters yesterday Brad Smith, Senior Vice President and General Counsel of Microsoft Corp, said:
"Over the past day and a half, we have given our perspective, providing information on things like multimedia technology and interoperability. We think it's been a very helpful and constructive exchange and we hope it's been helpful to the people who need to make these decisions."
He added:
"I do really want to underscore one point, which is that we have come to Brussels not only to discuss the issues but to work things out."
The remainder of the proceedings has been given over to presentations from rivals and critics of Microsoft, including Novell and Sun Microsystems. Two industry organisations, one backed by Microsoft, will also speak to the Commission.
A ruling is not expected until Spring next year.