Less verbose Server: response header from Apache
Unfortunately it's not possible to remove the Server: Apache header altogether from Apache's responses, but you can make them less verbose (and stop telling the whole world which version of Apache, OS and modules you're running).
httpd.conf, change (or add) these lines:
ServerTokens Prod ServerSignature Off
The first line changes the Server: header to only say “Apache” and nothing else. The second line disables the module listing on Apache-generated error pages.