Para desabilitar o X-Powered-By basta editar o arquivo php.ini e aplicar:
expose_php = off
Para desabilitar o Server no Apache, temos:
ServerTokens Full (or not specified)
Server sends (e.g.): Server: Apache/2.4.2 (Unix) PHP/4.2.2 MyMod/1.2
ServerTokens Prod[uctOnly]
Server sends (e.g.): Server: Apache
ServerTokens Major
Server sends (e.g.): Server: Apache/2
ServerTokens Minor
Server sends (e.g.): Server: Apache/2.4
ServerTokens Min[imal]
Server sends (e.g.): Server: Apache/2.4.2
ServerTokens OS
Server sends (e.g.): Server: Apache/2.4.2 (Unix)
O ideal é utilizar o ServerTokens Prod.
Abraços a todos,