for lazy bones here is an excerpt from the article:
When we request www.microsoft.com the DNS directs us to a server operated by Akamai. If you repeat this test, note that the actual Akamai server you connect to will differ according to your location on the internet and may vary from request to request. Akamai’s http caching servers run Linux, and so we report Linux as the operating system. However Akamai also forwards the http Server: header from the original server as part of the cached content, and so we report “Microsoft-IIS/6.0†as the web server.