Have you ever noticed that IIS tends to brand every HTTP response with the header X-Powered-By: ASP.NET - it will do this even if your site is not powered by ASP.NET!

Here's how to remove this header on IIS 6:

1. Open up the IIS Management Console
2. Right Click on a Web Sites and select Properties
3. Click on the HTTP Headers Tab
4. Under Custom HTTP Headers click on X-Powered-By: ASP.NET and click Remove

Here's how to remove it on IIS 7 / 7.5:

1. Open Server Manager and select the server name under Internet Information Services (IIS) Manager
2. Double click HTTP Response Headers
3. Remove the X-Powered-By header if it exists

Thanks go to Nick Gleason for sending instructions and providing a screenshot for IIS 7