Critics have bashed Microsoft's offer to license parts of its Windows source code, claiming that the move is a "poison pill" for open-source projects, and their work to improve interoperability with Windows.

"The move is less appealing than it seems up front," said Carlo Piana, an attorney representing the Free Software Foundation Europe (FSFE) in the anti-trust case. "We only need the compatibility information, nothing more, nothing less, and the ability to legally use it."
Microsoft defends the move, claiming that they have put their most valuable intellectual property on the table as a way of ensuring that third parties have everything they need to ensure interoperability with Windows. But critics have claimed that the offer of source code seems particularly designed to lock out open-source software.