A Harvard law professor filed a much-anticipated analysis of the Microsoft antitrust case on Tuesday, suggesting a way the presiding judge could find the company's practices illegal.

Berkman Professor of Entrepreneurial Studies Lawrence Lessig, an expert in the field of cyber-law at Harvard Law School (HLS) and a fellow of HLS's Berkman Center for Internet and Society, offered his friend-of-the-court brief at the request of U.S. District Judge Thomas Penfield Jackson.

Although Lessig's filing did not technically advocate for either side, Microsoft had officially protested Jackson's decision to seek Lessig's advice and the U.S. Department of Justice had filed a brief supporting the professor's role. Jackson overruled Microsoft's objection.

Lessig's filing is widely seen as supporting the government, because of his argument that Jackson could disregard a 1998 federal appeals court's ruling. The 1998 case ruled Microsoft could bundle its Web browser, Internet Explorer and its Windows operating system if there was a "plausible claim" that consumers benefit from having both products together.

Lessig considered one issue in particular--whether Microsoft engaged in illegal "tying," by integrating Internet Explorer into Windows. Tying refers to a firm selling one product and requiring the buyer to purchase a different, "tied" product.

The Justice Department, along with 19 state attorneys general, has accused Microsoft of forcing computer manufacturing firms to buy a Windows version which includes the Explorer browser.

Microsoft has argued that Internet Explorer is so tightly integrated into Windows that the two are not separate products. The close relationship between the Internet and operating system products allows consumers to browse files on their computers' hard drives as easily as they view Web pages.

The firm has also argued that computer programmers can more easily develop programs that need to communicate with Internet Explorer and Windows because Microsoft provides ready-made computer code.