http://httpd.apache.org/docs/2.2/mod/core.html#servertokens

This directive controls whether Server response header field which is sent back to clients includes a description of the generic OS-type of the server as well as information about compiled-in modules.

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/2.0

ServerTokens Min[imal]

Server sends (e.g.): Server: Apache/2.0.41

ServerTokens OS

Server sends (e.g.): Server: Apache/2.0.41 (Unix)

ServerTokens Full (or not specified)

Server sends (e.g.): Server: Apache/2.0.41 (Unix) PHP/4.2.2 MyMod/1.2

This setting applies to the entire server, and cannot be enabled or disabled on a virtualhost-by-virtualhost basis.

After version 2.0.44, this directive also controls the information presented by the ServerSignature directive.