Microsoft has become a 'platinum' sponsor of the Apache Software Foundation (ASF).

The Apache web server is an open source rival to Microsoft's Internet Information Server (IIS).

The surprise announcement was made during the Oscon open source convention in Portland, Oregon late last week.

"We thank Microsoft for their generous sponsorship that goes towards supporting the ASF and the over 60 top-level projects in use and development within the ASF," said ASF chairman Jim Jagielski.

"The ASF Sponsorship programme is an excellent way for companies and organisations to show their commitment and enthusiasm towards the ASF and 'The Apache Way'.

"It also helps to ensure that highly innovative, freely available and community-based/consensus-developed software can continue to flourish and thrive within one of the most successful and respected communities in open source."

Microsoft has stressed that this is not a move away from its IIS platform, highlighting the recent addition of support for PHP. The company added that development of IIS 8 is currently under way.

Platinum sponsorship requires a donation level of $100,000 per year.