Microsoft has announced that it is releasing more than 20,000 lines of code under the General Public Licence (GPL).

The code includes three Linux device drivers and is designed to help Linux users running virtualised operating systems on Windows Server 2008 Hyper-V or Windows Server 2008 R2 Hyper-V.

"Many people are surprised when they hear how much open source community and development work is happening across Microsoft," said Sam Ramji, senior director of platform strategy at Microsoft.

"This probably has a lot to do with the fact that we are focused on getting the work done, and engaging with communities on a one-to-one basis, rather than promoting it. We currently participate and collaborate on a number of open-source projects through contributions of technical support and code."

Ramji cited Microsoft's extensive work with the PHP community as an example, as well as work to ensure operating system compatibility with Firefox and continuing work on the Apache project.

However, the move to GPL is quite a turnaround for Microsoft, which once declared the GPL an "un-American cancer". Microsoft claimed that it made the move after requests from customers.