Chapter 10 Install and System Administration for FortiOS 5.0 : Advanced concepts : Obfuscate HTTP responses
  
Obfuscate HTTP responses
The FortiGate unit can obfuscate the HTTP responses from the FortiGate admin GUI and SSL VPN servers. By default this option is not enabled. To obfuscate HTTP headers, use the following CLI command:
config system global
set http-obfucate {none | header-only | modified | no-error}
end
Where:
none — do not hide the FortiGate web server identity.
header-only — hides the HTTP server banner.
modified — provides modified error responses.
no-error — suppresses error responses.